Planarization of overcoat layer on slanted surface-relief structures

ABSTRACT

Techniques for producing an overcoat layer on slanted surface-relief structures and devices obtained using the techniques are disclosed. In some embodiments, a method of planarizing an overcoat layer over a surface-relief structure includes removing a portion of the overcoat layer using an ion beam at a glancing angle. The overcoat layer includes planar surface portions and non-planar surface portions. Each of the non-planar surface portions includes a first sloped side and a second sloped side facing the first sloped side. The glancing angle is selected such that the first sloped side of each non-planar surface portion is shadowed from the ion beam by an adjacent planar surface portion such that the ion beam does not reach at least the first sloped side of each non-planar surface portion but reaches the second sloped side of each non-planar surface portion.

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.62/786,143, filed Dec. 28, 2018, entitled “PLANARIZATION OF OVERCOATLAYER ON SLANTED SURFACE-RELIEF STRUCTURES”, which is assigned to theassignee hereof, and incorporated by reference herein in its entirety.

BACKGROUND

An artificial reality system, such as a head-mounted display (HMD) orheads-up display (HUD) system, generally includes a display configuredto present artificial images that depict objects in a virtualenvironment. The display may display virtual objects or combine imagesof real objects with virtual objects, as in virtual reality (VR),augmented reality (AR), or mixed reality (MR) applications. For example,in an AR system, a user may view both images of virtual objects (e.g.,computer-generated images (CGIs)) and the surrounding environment by,for example, seeing through transparent display glasses or lenses (oftenreferred to as optical see-through) or viewing displayed images of thesurrounding environment captured by a camera (often referred to as videosee-through).

One example optical see-through AR system may use a waveguide-basedoptical display, where light of projected images may be coupled into awaveguide (e.g., a substrate), propagate within the waveguide, and becoupled out of the waveguide at different locations. In someimplementations, the light of the projected images may be coupled intoor out of the waveguide using a diffractive optical element, such as aslanted surface-relief grating. In many cases, it may be challenging tocost-effectively fabricate the slanted surface-relief grating.

SUMMARY

This disclosure relates generally to techniques for producing anovercoat layer on slanted surface-relief structures. Slantedsurface-relief structures, such as slanted surface-relief gratings, mayinclude ridges and grooves. An overcoat layer may be formed over theslanted surface-relief gratings filling the grooves and covering theridges. According to certain embodiments, planarization operations maybe performed to achieve a flat top surface of the overcoat layer.

In some embodiments, deposition and etching operations may be performedin each of multiple processing cycles. In some embodiments, ion beametching may be utilized to improve the surface finishing of the overcoatlayer. In some embodiments, chemical-mechanical planarization techniquesmay be used to obtain an even or flat surface after an overcoat layerhas been formed on the surface-relief structures.

In some embodiments, after the grooves have been filled by an overcoatmaterial using ALD or other cyclic deposition process, a spin-coatingoperation may be performed to obtain a substantially flat surface of theovercoat layer. In some embodiments, following the spin-coatingoperation, an etching operation may be performed to remove all of theovercoat material applied using the spin-coating operation and to removeat least a portion of the overcoat material deposited using the ALD orother cyclic process to achieve a substantially flat surface of theovercoat layer.

In some embodiments, a method of planarizing an overcoat layer over asurface-relief structure on a substrate may include removing a portionof the overcoat layer using an ion beam at a glancing angle. Theovercoat layer may include a plurality of planar surface portions and aplurality of non-planar surface portions. Each of the plurality ofnon-planar surface portions may include a first sloped side and a secondsloped side facing the first sloped side. The glancing angle may be anangle between the ion beam and the plurality of planar surface portions.The glancing angle may be selected such that the first sloped side ofeach of the plurality of non-planar surface portions may be shadowedfrom the ion beam by an adjacent planar surface portion of the pluralityof planar surface portions such that the ion beam may not reach at leastthe first sloped side of each of the plurality of non-planar surfaceportions but may reach the second sloped side of each of the pluralityof non-planar surface portions.

In some embodiments, the plurality of non-planar surface portions may beconcave. Each of the plurality of non-planar surface portions mayfurther include a bottom between the first sloped side and the secondsloped side. The glancing angle may be further selected such that theion beam may not reach the bottom of each of the plurality of non-planarsurface portions. In some embodiments, the first sloped side of each ofthe plurality of non-planar surface portions may be oriented at a firstangle relative to an adjacent planar surface portion of the plurality ofplanar surface portions. The glancing angle may be less than the firstangle. In some embodiments, the glancing angle may range between 1° and15°. In some embodiments, removing the portion of the overcoat layerusing the ion beam may include reducing the glancing angle as theportion of the overcoat layer is being removed by the ion beam. In someembodiments, the glancing angle may be reduced from 15° to less than 1°.

In some embodiments, the surface-relief structure may include aplurality of ridges slanted with respect to the substrate, and aplurality of grooves each between two adjacent ridges. In someembodiments, the plurality of grooves may each have a depth that may beat least 100 nm. In some embodiments, the plurality of ridges may eachhave a slant angle that may be at least 45°. In some embodiments, theovercoat layer may be deposited over the surface-relief structure usingan atomic layer deposition process.

In some embodiments, a method of forming an overcoat layer over asurface-relief structure on a substrate, the method may includereceiving the substrate. The surface-relief structure may include aplurality of ridges slanted with respect to the substrate, and aplurality of grooves each between two adjacent ridges. The method mayfurther include depositing, in each cycle of a plurality of cycles, auniform layer of a first overcoat material on surfaces of the pluralityof ridges and bottoms of the plurality of grooves. The method may alsoinclude depositing a second overcoat material over the layers of thefirst overcoat material using a spin-coating process.

In some embodiments, the plurality of ridges may each have a slant anglethat may be at least 45°. In some embodiments, only one atomic layer ofthe first overcoat material may be deposited in each cycle. In someembodiments, a refractive index of the second overcoat material maymatch a refractive index of the first overcoat material.

In some embodiments, the method may further include removing the secondovercoat material deposited over the first overcoat material to exposethe first overcoat material deposited over the surface-relief structure.The method may further include removing a portion of the first overcoatmaterial to obtain a planar top surface of the first overcoat material.

In some embodiments, removing the second overcoat material and/or theportion of the first overcoat material may include removing the secondovercoat material and/or the portion of the first overcoat materialusing a chemical-mechanical polishing process. In some embodiments,removing the second overcoat material and/or the portion of the firstovercoat material may include removing the second overcoat materialand/or the portion of the first overcoat material using a glancing ionbeam etching. In some embodiments, removing the second overcoat materialand/or the portion of the first overcoat material may include removingthe second overcoat material and/or the portion of the first overcoatmaterial using a dry etching process. In some embodiments, the dryetching process may etch the first overcoat material and the secondovercoat material at the same rate.

In some embodiments, the method may further include, in each cycle,after depositing the uniform layer of the first overcoat material,removing portions of the uniform layer of the first overcoat materialdeposited on top surfaces of the plurality of ridges.

In some embodiments, a waveguide may include a substrate, asurface-relief structure on the substrate, and an overcoat layer on thesurface-relief structure. The surface-relief structure may include aplurality of ridges slanted with respect to the substrate, and aplurality of grooves each defined by two adjacent ridges. The overcoatlayer and the plurality of ridges may collectively form a light-couplingstructure on the substrate. A top surface of the overcoat layer may beobtained by ion beam etching at a glancing angle.

In some embodiments, the ion beam etching may be performed after anatomic layer deposition operation where layers of an overcoat materialmay be deposited to form an intermediate overcoat layer. In someembodiments, the ion beam etching may be performed to remove a pluralityof non-planar surface portions on an intermediate overcoat layer. Eachof the plurality of non-planar surface portions may include a firstsloped side and a second sloped side facing the first sloped side. Theglancing angle may be selected such that the first sloped side of eachof the plurality of non-planar surface portions may be shadowed from theion beam and the second sloped side of each of the plurality ofnon-planar surface portions may be exposed to the ion beam.

This summary is neither intended to identify key or essential featuresof the claimed subject matter, nor is it intended to be used inisolation to determine the scope of the claimed subject matter. Thesubject matter should be understood by reference to appropriate portionsof the entire specification of this disclosure, any or all drawings, andeach claim. The foregoing, together with other features and examples,will be described in more detail below in the following specification,claims, and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Illustrative embodiments are described in detail below with reference tothe following figures.

FIG. 1 is a simplified diagram of an example near-eye display accordingto certain embodiments.

FIG. 2 is a cross-sectional view of an example near-eye displayaccording to certain embodiments.

FIG. 3 is an isometric view of an example waveguide display according tocertain embodiments.

FIG. 4 is a cross-sectional view of an example waveguide displayaccording to certain embodiments.

FIG. 5 is a simplified block diagram of an example artificial realitysystem including a waveguide display.

FIG. 6 illustrates an example optical see-through augmented realitysystem using a waveguide display according to certain embodiments;

FIG. 7 illustrates propagations of display light and external light inan example waveguide display.

FIG. 8 illustrates an example slanted grating coupler in an examplewaveguide display according to certain embodiments.

FIG. 9A illustrates an example slanted grating coupler in an examplewaveguide display according to certain embodiments.

FIG. 9B illustrates the example slanted grating coupler of FIG. 9A thathas been coated with a layer of overcoat material according to certainembodiments.

FIG. 9C illustrates the example slanted grating coupler of FIGS. 9A and9B that has been coated with additional overcoat material according tocertain embodiments.

FIG. 9D illustrates the example slanted grating coupler of FIGS. 9A-9Cthat has been further coated with additional overcoat material to form aplanar overcoat layer according to certain embodiments.

FIG. 10 is a simplified flow chart illustrating an example process forovercoating a slanted surface-relief structure according to certainembodiments.

FIG. 11 illustrates an example of a slanted surface-relief structurewith an overcoat layer according to certain embodiments.

FIG. 12 is a simplified flow chart illustrating an example process forovercoating a slanted surface-relief structure according to certainembodiments.

FIG. 13A illustrates an example slanted grating coupler that is coatedwith a layer of overcoat material according to certain embodiments.

FIG. 13B illustrates the example slanted grating coupler of FIG. 13A,where portions of the layer of overcoat material have been removedaccording to certain embodiments.

FIG. 13C illustrates the example slanted grating coupler of FIGS. 13Aand 13B that has been coated with additional overcoat material accordingto certain embodiments.

FIG. 13D illustrates the example slanted grating coupler with of FIGS.13A-13C that has been further coated with additional overcoat materialto form a planar overcoat layer according to certain embodiments.

FIG. 14 is a simplified flow chart illustrating an example process forplanarizing an overcoat layer on a slanted surface-relief structureaccording to certain embodiments.

FIG. 15A illustrates an example slanted grating coupler that is coatedwith a layer of overcoat material according to certain embodiments.

FIG. 15B illustrates the example slanted grating coupler of FIG. 15A,where portions of the layer of overcoat material have been removedaccording to certain embodiments.

FIG. 15C illustrates the example slanted grating coupler of FIGS. 15Aand 15B, where additional portions of the layer of overcoat materialhave been removed according to certain embodiments.

FIG. 15D illustrates the example slanted grating coupler of FIGS.15A-15C, where additional portions of the layer of overcoat materialhave been further removed to form a planar overcoat layer according tocertain embodiments.

FIG. 16A is a simplified flow chart illustrating an example process forplanarizing an overcoat layer on a slanted surface-relief structureaccording to certain embodiments.

FIG. 16B is a simplified flow chart illustrating an example process forplanarizing an overcoat layer on a slanted surface-relief structureaccording to certain embodiments.

FIG. 17A illustrates an example slanted grating coupler that is coatedwith a layer of overcoat material according to certain embodiments.

FIG. 17B illustrates the example slanted grating coupler of FIG. 17Athat has been coated with additional overcoat material to form a planarovercoat layer according to certain embodiments.

FIG. 18A illustrates an example slanted grating coupler that is coatedwith a layer of overcoat material according to certain embodiments.

FIG. 18B illustrates the example slanted grating coupler of FIG. 18Athat has been coated with additional overcoat material according tocertain embodiments.

FIG. 18C illustrates the example slanted grating coupler of FIGS. 18Aand 18B, where portions of the overcoat material have been removedaccording to certain embodiments.

FIG. 18D illustrates the example slanted grating coupler of FIGS.18A-18C, where additional portions of the overcoat material have beenremoved to form a planar overcoat layer according to certainembodiments.

FIG. 19 is a simplified block diagram of an example electronic system ofan example near-eye display according to certain embodiments.

The figures depict embodiments of the present disclosure for purposes ofillustration only. One skilled in the art will readily recognize fromthe following description that alternative embodiments of the structuresand methods illustrated may be employed without departing from theprinciples, or benefits touted, of this disclosure.

In the appended figures, similar components and/or features may have thesame reference label. Further, various components of the same type maybe distinguished by following the reference label by a dash and a secondlabel that distinguishes among the similar components. If only the firstreference label is used in the specification, the description isapplicable to any one of the similar components having the same firstreference label irrespective of the second reference label.

DETAILED DESCRIPTION

This disclosure relates to waveguide-based near-eye display systems.More specifically, and without limitation, this disclosure relates toplanarization techniques for an overcoat layer covering slantedsurface-relief structures.

Slanted surface-relief structures, such as slanted surface-reliefgratings, may be used in many optical or electronic devices tomanipulate behavior of light and/or electricity. According to certainembodiments, slanted surface-relief gratings may be used in some opticaldevices, such as near-eye display systems in artificial realityapplications, to create high refractive index variations, highdiffraction efficiencies, and/or high light transfer efficiencies. Theslanted surface-relief gratings may include ridges and grooves. Toprotect the structure of the slanted surface-relief gratings and toincrease field of view and reduce rainbow artifacts, etc., an overcoatlayer may be formed over the slanted surface-relief gratings. Theovercoat material may have a refractive index different from that of thematerial forming the ridges. The ridges and the overcoat materialfilling the grooves and covering the ridges may function together as agrating coupler for the waveguide display.

Spin-on techniques may offer a relatively low-cost and simple option,but the overcoat material may not be evenly coated cross the slantedsurface-relief gratings partly due to the varying configuration of thegratings, such as the varying slant angle of the ridges, the varyingduty cycle of the gratings, the varying depth of the grooves defined bythe ridges, and the like. When the slant angle of the ridges may becomerelatively large, it may become more difficult to achieve a uniformovercoat. The thickness variation can cause significant loss ofthroughput due to stray light paths. Further, the grooves may be quitenarrow and/or deep in some applications, and when spin-on techniques areutilized, solvent trapping may occur in, for example, the grooves. Thetrapped solvent can lead to varying refractive index within the overcoatlayer and efficiency loss of the device.

According to certain embodiments, atomic layer deposition (ALD) may beutilized to improve the flatness/evenness of the surface profile and theuniformity of the refractive index of the overcoat layer. In someembodiments, the top surface of the overcoat layer may still includedips or unevenness. For certain applications, planarization operationsmay be performed to achieve a flat top surface of the overcoat layer.

In some embodiments, deposition and etching operations may be performedin each of multiple processing cycles. The deposition operation mayinclude ALD. In each processing cycle, a thin overcoat material layermay be deposited on exposed surfaces during the deposition operation,and the etching operation may remove the overcoat material deposited ontop of the ridges faster than the overcoat material deposited in thegrooves such that at least some overcoat materials deposited in thegrooves during the deposition operation may remain while the overcoatmaterials on the top of the ridges may be removed. As a result, uponcompletion of the multiple operation and etching cycles, a substantiallyflat or even top surface of the overcoat layer can be achieved.

In some embodiments, ion beam etching may be utilized to improve thesurface finishing of the overcoat layer. For example, a glancing ionbeam that may be nearly parallel to the surface of the overcoat materialdeposited can be used to remove the overcoat material beyond the dipsfaster than the overcoat material within the dips such that an even orflat surface of the overcoat layer may be obtained. In some embodiments,the glancing angle of the ion beam may gradually decrease as theovercoat material is being etched away and the depth of the dipsgradually reduces.

In some embodiments, chemical-mechanical planarization technique may beused to obtain an even or flat surface after an overcoat layer has beenformed on the surface-relief structures.

In some embodiments, after the grooves have been filled using ALD orother cyclic deposition process, a spin-coating operation may beperformed. Because upon completion of the ALD or other cyclic depositionprocess, the surface evenness has been significantly improved ascompared to a non-coated substrate with varying gratings formed thereon,a substantially flat surface may be obtained by the subsequentspin-coating operation. In some embodiments, the overcoat material usedfor the spin-coating operation may have a refractive index matching thatof the overcoat material deposited using ALD.

In some embodiments, the overcoat material used for the spin-coatingoperation may have a different refractive index from that of theovercoat material deposited using ALD or other cyclic process, but mayhave about 1:1 etch selectivity with respect to the overcoat materialapplied using the ALD or other cyclic process. Following thespin-coating operation, an etching operation may be performed to removeall of the overcoat material applied using the spin-coating operationand to remove at least the overcoat material above the bottom of thedips formed during the ALD process to achieve a substantially flatsurface of the overcoat layer.

In the following description, for the purposes of explanation, specificdetails are set forth in order to provide a thorough understanding ofexamples of the disclosure. However, it will be apparent that variousexamples may be practiced without these specific details. For example,devices, systems, structures, assemblies, methods, and other componentsmay be shown as components in block diagram form in order not to obscurethe examples in unnecessary detail. In other instances, well-knowndevices, processes, systems, structures, and techniques may be shownwithout necessary detail in order to avoid obscuring the examples. Thefigures and description are not intended to be restrictive. The termsand expressions that have been employed in this disclosure are used asterms of description and not of limitation, and there is no intention inthe use of such terms and expressions of excluding any equivalents ofthe features shown and described or portions thereof. The word “example”is used herein to mean “serving as an example, instance, orillustration.” Any embodiment or design described herein as “example” isnot necessarily to be construed as preferred or advantageous over otherembodiments or designs.

FIG. 1 is a simplified diagram of an example near-eye display 100according to certain embodiments. Near-eye display 100 may present mediato a user. Examples of media presented by near-eye display 100 mayinclude one or more images, video, and/or audio. In some embodiments,audio may be presented via an external device (e.g., speakers and/orheadphones) that receives audio information from near-eye display 100, aconsole, or both, and presents audio data based on the audioinformation. Near-eye display 100 is generally configured to operate asan artificial reality display. In some embodiments, near-eye display 100may operate as an augmented reality (AR) display or a mixed reality (MR)display.

Near-eye display 100 may include a frame 105 and a display 110. Frame105 may be coupled to one or more optical elements. Display 110 may beconfigured for the user to see content presented by near-eye display100. In some embodiments, display 110 may include a waveguide displayassembly for directing light from one or more images to an eye of theuser.

FIG. 2 is a cross-sectional view 200 of near-eye display 100 illustratedin FIG. 1. Display 110 may include at least one waveguide displayassembly 210. An exit pupil 230 may be located at a location where auser's eye 220 is positioned when the user wears near-eye display 100.For purposes of illustration, FIG. 2 shows cross-sectional view 200associated with user's eye 220 and a single waveguide display assembly210, but, in some embodiments, a second waveguide display may be usedfor the second eye of the user.

Waveguide display assembly 210 may be configured to direct image light(i.e., display light) to an eyebox located at exit pupil 230 and touser's eye 220. Waveguide display assembly 210 may include one or morematerials (e.g., plastic, glass, etc.) with one or more refractiveindices. In some embodiments, near-eye display 100 may include one ormore optical elements between waveguide display assembly 210 and user'seye 220.

In some embodiments, waveguide display assembly 210 may include a stackof one or more waveguide displays including, but not restricted to, astacked waveguide display, a varifocal waveguide display, etc. Thestacked waveguide display is a polychromatic display (e.g., ared-green-blue (RGB) display) created by stacking waveguide displayswhose respective monochromatic sources are of different colors. Thestacked waveguide display may also be a polychromatic display that canbe projected on multiple planes (e.g. multi-planar colored display). Insome configurations, the stacked waveguide display may be amonochromatic display that can be projected on multiple planes (e.g.multi-planar monochromatic display). The varifocal waveguide display isa display that can adjust a focal position of image light emitted fromthe waveguide display. In alternate embodiments, waveguide displayassembly 210 may include the stacked waveguide display and the varifocalwaveguide display.

FIG. 3 is an isometric view of an embodiment of a waveguide display 300.In some embodiments, waveguide display 300 may be a component (e.g.,waveguide display assembly 210) of near-eye display 100. In someembodiments, waveguide display 300 may be part of some other near-eyedisplays or other systems that may direct image light to a particularlocation.

Waveguide display 300 may include a source assembly 310, an outputwaveguide 320, and a controller 330. For purposes of illustration, FIG.3 shows waveguide display 300 associated with a user's eye 390, but insome embodiments, another waveguide display separate, or partiallyseparate, from waveguide display 300 may provide image light to anothereye of the user.

Source assembly 310 may generate image light 355 for display to theuser. Source assembly 310 may generate and output image light 355 to acoupling element 350 located on a first side 370-1 of output waveguide320. In some embodiments, coupling element 350 may couple image light355 from source assembly 310 into output waveguide 320. Coupling element350 may include, for example, a diffraction grating, a holographicgrating, one or more cascaded reflectors, one or more prismatic surfaceelements, and/or an array of holographic reflectors. Output waveguide320 may be an optical waveguide that can output expanded image light 340to user's eye 390. Output waveguide 320 may receive image light 355 atone or more coupling elements 350 located on first side 370-1 and guidereceived image light 355 to a directing element 360.

Directing element 360 may redirect received input image light 355 todecoupling element 365 such that received input image light 355 may becoupled out of output waveguide 320 via decoupling element 365.Directing element 360 may be part of, or affixed to, first side 370-1 ofoutput waveguide 320. Decoupling element 365 may be part of, or affixedto, a second side 370-2 of output waveguide 320, such that directingelement 360 is opposed to decoupling element 365. Directing element 360and/or decoupling element 365 may include, for example, a diffractiongrating, a holographic grating, a surface-relief grating, one or morecascaded reflectors, one or more prismatic surface elements, and/or anarray of holographic reflectors.

Second side 370-2 of output waveguide 320 may represent a plane along anx-dimension and a y-dimension. Output waveguide 320 may include one ormore materials that can facilitate total internal reflection of imagelight 355. Output waveguide 320 may include, for example, silicon,plastic, glass, and/or polymers. Output waveguide 320 may have arelatively small form factor. For example, output waveguide 320 may beapproximately 50 mm wide along the x-dimension, about 30 mm long alongthe y-dimension, and about 0.5 to 1 mm thick along a z-dimension.

Controller 330 may control scanning operations of source assembly 310.Controller 330 may determine scanning instructions for source assembly310. In some embodiments, output waveguide 320 may output expanded imagelight 340 to user's eye 390 with a large field of view (FOV). Forexample, expanded image light 340 provided to user's eye 390 may have adiagonal FOV (in x and y) of about 60 degrees or greater and/or about150 degrees or less. Output waveguide 320 may be configured to providean eyebox with a length of about 20 mm or greater and/or equal to orless than about 50 mm, and/or a width of about 10 mm or greater and/orequal to or less than about 50 mm.

FIG. 4 is a cross-sectional view 400 of waveguide display 300. Waveguidedisplay 300 may include source assembly 310 and output waveguide 320.Source assembly 310 may generate image light 355 (i.e., display light)in accordance with scanning instructions from controller 330. Sourceassembly 310 may include a source 410 and an optics system 415. Source410 may include a light source that generates coherent or partiallycoherent light. Source 410 may include, for example, a laser diode, avertical cavity surface emitting laser, and/or a light emitting diode.

Optics system 415 may include one or more optical components that cancondition the light from source 410. Conditioning light from source 410may include, for example, expanding, collimating, and/or adjustingorientation in accordance with instructions from controller 330. The oneor more optical components may include one or more lenses, liquidlenses, mirrors, apertures, and/or gratings. Light emitted from opticssystem 415 (and also source assembly 310) may be referred to as imagelight 355 or display light.

Output waveguide 320 may receive image light 355 from source assembly310. Coupling element 350 may couple image light 355 from sourceassembly 310 into output waveguide 320. In embodiments where couplingelement 350 includes a diffraction grating, the diffraction grating maybe configured such that total internal reflection may occur withinoutput waveguide 320, and thus image light 355 coupled into outputwaveguide 320 may propagate internally within output waveguide 320(e.g., by total internal reflection) toward decoupling element 365.

Directing element 360 may redirect image light 355 toward decouplingelement 365 for coupling at least a portion of the image light out ofoutput waveguide 320. In embodiments where directing element 360 is adiffraction grating, the diffraction grating may be configured to causeincident image light 355 to exit output waveguide 320 at angle(s) ofinclination relative to a surface of decoupling element 365. In someembodiments, directing element 360 and/or the decoupling element 365 maybe structurally similar.

Expanded image light 340 exiting output waveguide 320 may be expandedalong one or more dimensions (e.g., elongated along the x-dimension). Insome embodiments, waveguide display 300 may include a plurality ofsource assemblies 310 and a plurality of output waveguides 320. Each ofsource assemblies 310 may emit a monochromatic image light correspondingto a primary color (e.g., red, green, or blue). Each of outputwaveguides 320 may be stacked together to output an expanded image light340 that may be multi-colored.

FIG. 5 is a simplified block diagram of an example artificial realitysystem 500 including waveguide display assembly 210. System 500 mayinclude near-eye display 100, an imaging device 535, and an input/outputinterface 540 that are each coupled to a console 510.

As described above, near-eye display 100 may be a display that presentsmedia to a user. Examples of media presented by near-eye display 100 mayinclude one or more images, video, and/or audio. In some embodiments,audio may be presented via an external device (e.g., speakers and/orheadphones) that may receive audio information from near-eye display 100and/or console 510 and present audio data based on the audio informationto a user. In some embodiments, near-eye display 100 may act as anartificial reality eyewear glass. For example, in some embodiments,near-eye display 100 may augment views of a physical, real-worldenvironment, with computer-generated elements (e.g., images, video,sound, etc.).

Near-eye display 100 may include waveguide display assembly 210, one ormore position sensors 525, and/or an inertial measurement unit (IMU)530. Waveguide display assembly 210 may include a waveguide display,such as waveguide display 300 that includes source assembly 310, outputwaveguide 320, and controller 330 as described above.

IMU 530 may include an electronic device that can generate fastcalibration data indicating an estimated position of near-eye display100 relative to an initial position of near-eye display 100 based onmeasurement signals received from one or more position sensors 525.

Imaging device 535 may generate slow calibration data in accordance withcalibration parameters received from console 510. Imaging device 535 mayinclude one or more cameras and/or one or more video cameras.

Input/output interface 540 may be a device that allows a user to sendaction requests to console 510. An action request may be a request toperform a particular action. For example, an action request may be tostart or end an application or to perform a particular action within theapplication.

Console 510 may provide media to near-eye display 100 for presentationto the user in accordance with information received from one or more ofimaging device 535, near-eye display 100, and input/output interface540. In the example shown in FIG. 5, console 510 may include anapplication store 545, a tracking module 550, and an engine 555.

Application store 545 may store one or more applications for executionby the console 510. An application may include a group of instructionsthat, when executed by a processor, may generate content forpresentation to the user. Examples of applications may include gamingapplications, conferencing applications, video playback application, orother suitable applications.

Tracking module 550 may calibrate system 500 using one or morecalibration parameters and may adjust one or more calibration parametersto reduce error in determination of the position of near-eye display100. Tracking module 550 may track movements of near-eye display 100using slow calibration information from imaging device 535. Trackingmodule 550 may also determine positions of a reference point of near-eyedisplay 100 using position information from the fast calibrationinformation.

Engine 555 may execute applications within system 500 and receivesposition information, acceleration information, velocity information,and/or predicted future positions of near-eye display 100 from trackingmodule 550. In some embodiments, information received by engine 555 maybe used for producing a signal (e.g., display instructions) to waveguidedisplay assembly 210. The signal may determine a type of content topresent to the user.

There may be many different ways to implement the waveguide display. Forexample, in some implementations, output waveguide 320 may include aslanted surface between first side 370-1 and second side 370-2 forcoupling image light 355 into output waveguide 320. In someimplementations, the slanted surface may be coated with a reflectivecoating to reflect light towards directing element 360. In someimplementations, the angle of the slanted surface may be configured suchthat image light 355 may be reflected by the slanted surface due tototal internal reflection. In some implementations, directing element360 may not be used, and light may be guided within output waveguide 320by total internal reflection. In some implementations, decouplingelements 365 may be located near first side 370-1.

In some implementations, output waveguide 320 and decoupling element 365(and directing element 360 if used) may be transparent to light from theenvironment, and may act as an optical combiner for combining imagelight 355 and light from the physical, real-world environment in frontof near-eye display 100. As such, the user can view both artificialimages of artificial objects from source assembly 310 and real images ofreal objects in the physical, real-world environment, which may bereferred to as optical see-through.

FIG. 6 illustrates an example optical see-through augmented realitysystem 600 using a waveguide display according to certain embodiments.Augmented reality system 600 may include a projector 610 and a combiner615. Projector 610 may include a light source or image source 612 andprojector optics 614. In some embodiments, image source 612 may includea plurality of pixels that displays virtual objects, such as an LCDdisplay panel or an LED display panel. In some embodiments, image source612 may include a light source that generates coherent or partiallycoherent light. For example, image source 612 may include a laser diode,a vertical cavity surface emitting laser, and/or a light emitting diode.In some embodiments, image source 612 may include a plurality of lightsources each emitting a monochromatic image light corresponding to aprimary color (e.g., red, green, or blue). In some embodiments, imagesource 612 may include an optical pattern generator, such as a spatiallight modulator. Projector optics 614 may include one or more opticalcomponents that can condition the light from image source 612, such asexpanding, collimating, scanning, or projecting light from image source612 to combiner 615. The one or more optical components may include, forexample, one or more lenses, liquid lenses, mirrors, apertures, and/orgratings. In some embodiments, projector optics 614 may include a liquidlens (e.g., a liquid crystal lens) with a plurality of electrodes thatallows scanning of the light from image source 612.

Combiner 615 may include an input coupler 630 for coupling light fromprojector 610 into a substrate 620 of combiner 615. Input coupler 630may include a volume holographic grating, a diffractive optical elements(DOE) (e.g., a surface-relief grating), or a refractive coupler (e.g., awedge or a prism). Input coupler 630 may have a coupling efficiency ofgreater than 30%, 50%, 75%, 90%, or higher for visible light. As usedherein, visible light may refer to light with a wavelength between about380 nm to about 750 nm. Light coupled into substrate 620 may propagatewithin substrate 620 through, for example, total internal reflection(TIR). Substrate 620 may be in the form of a lens of a pair ofeyeglasses. Substrate 620 may have a flat or a curved surface, and mayinclude one or more types of dielectric materials, such as glass,quartz, plastic, polymer, poly(methyl methacrylate) (PMMA), crystal, orceramic. A thickness of the substrate may range from, for example, lessthan about 1 mm to about 10 mm or more. Substrate 620 may be transparentto visible light. A material may be “transparent” to a light beam if thelight beam can pass through the material with a high transmission rate,such as larger than 50%, 60%, 75%, 80%, 90%, 95%, or higher, where asmall portion of the light beam (e.g., less than 50%, 40%, 25%, 20%,10%, 5%, or less) may be scattered, reflected, or absorbed by thematerial. The transmission rate (i.e., transmissivity) may berepresented by either a photopically weighted or an unweighted averagetransmission rate over a range of wavelengths, or the lowesttransmission rate over a range of wavelengths, such as the visiblewavelength range.

Substrate 620 may include or may be coupled to a plurality of outputcouplers 640 configured to extract at least a portion of the lightguided by and propagating within substrate 620 from substrate 620, anddirect extracted light 660 to an eye 690 of the user of augmentedreality system 600. As input coupler 630, output couplers 640 mayinclude grating couplers (e.g., volume holographic gratings orsurface-relief gratings), other DOEs, prisms, etc. Output couplers 640may have different coupling (e.g., diffraction) efficiencies atdifferent locations. Substrate 620 may also allow light 650 fromenvironment in front of combiner 615 to pass through with little or noloss. Output couplers 640 may also allow light 650 to pass through withlittle loss. For example, in some implementations, output couplers 640may have a low diffraction efficiency for light 650 such that light 650may be refracted or otherwise pass through output couplers 640 withlittle loss, and thus may have a higher intensity than extracted light660. In some implementations, output couplers 640 may have a highdiffraction efficiency for light 650 and may diffract light 650 tocertain desired directions (i.e., diffraction angles) with little loss.As a result, the user may be able to view combined images of theenvironment in front of combiner 615 and virtual objects projected byprojector 610.

FIG. 7 illustrates propagations of incident display light 740 andexternal light 730 in an example waveguide display 700 including awaveguide 710 and a grating coupler 720. Waveguide 710 may be a flat orcurved transparent substrate with a refractive index n₂ greater than thefree space refractive index n₁ (i.e., 1.0). Grating coupler 720 mayinclude, for example, a Bragg grating or a surface-relief grating.

Incident display light 740 may be coupled into waveguide 710 by, forexample, input coupler 630 of FIG. 6 or other couplers (e.g., a prism orslanted surface) described above. Incident display light 740 maypropagate within waveguide 710 through, for example, total internalreflection. When incident display light 740 reaches grating coupler 720,incident display light 740 may be diffracted by grating coupler 720into, for example, a 0^(th) order diffraction (i.e., reflection) light742 and a −1st order diffraction light 744. The 0^(th) order diffractionmay continue to propagate within waveguide 710, and may be reflected bythe bottom surface of waveguide 710 towards grating coupler 720 at adifferent location. The −1st order diffraction light 744 may be coupled(e.g., refracted) out of waveguide 710 towards the user's eye, because atotal internal reflection condition may not be met at the bottom surfaceof waveguide 710 due to the diffraction angle of the −1^(st) orderdiffraction light 744.

External light 730 may also be diffracted by grating coupler 720 into,for example, a 0^(th) order diffraction light 732 or a −1st orderdiffraction light 734. The 0^(th) order diffraction light 732 or the−1st order diffraction light 734 may be refracted out of waveguide 710towards the user's eye. Thus, grating coupler 720 may act as an inputcoupler for coupling external light 730 into waveguide 710, and may alsoact as an output coupler for coupling incident display light 740 out ofwaveguide 710. As such, grating coupler 720 may act as a combiner forcombining external light 730 and incident display light 740 and send thecombined light to the user's eye.

In order to diffract light at a desired direction towards the user's eyeand to achieve a desired diffraction efficiency for certain diffractionorders, grating coupler 720 may include a blazed or slanted grating,such as a slanted Bragg grating or surface-relief grating, where thegrating ridges and grooves may be tilted relative to the surface normalof grating coupler 720 or waveguide 710.

FIG. 8 illustrates an example slanted grating 820 in an examplewaveguide display 800 according to certain embodiments. Waveguidedisplay 800 may include slanted grating 820 on a waveguide 810, such assubstrate 620. Slanted grating 820 may act as a grating coupler forcouple light into or out of waveguide 810. In some embodiments, slantedgrating 820 may include a periodic structure with a period p. Forexample, slanted grating 820 may include a plurality of ridges 822 andgrooves 824 between ridges 822. Each period of slanted grating 820 mayinclude a ridge 822 and a groove 824, which may be an air gap or aregion filled with a material with a refractive index n_(g2). The ratiobetween the width of a ridge 822 and the grating period p may bereferred to as duty cycle. Slanted grating 820 may have a duty cycleranging, for example, from about 10% to about 90% or greater. In someembodiments, the duty cycle may vary from period to period. In someembodiments, the period p of the slanted grating may vary from one areato another on slanted grating 820, or may vary from one period toanother (i.e., chirped) on slanted grating 820.

Ridges 822 may be made of a material with a refractive index of n_(g1),such as silicon containing materials (e.g., SiO₂, Si₃N₄, SiC,SiO_(x)N_(y), or amorphous silicon), organic materials (e.g., spin oncarbon (SOC) or amorphous carbon layer (ACL) or diamond like carbon(DLC)), or inorganic metal oxide layers (e.g., TiO_(x), AlO_(x),TaO_(x), HfO_(x), etc.). Each ridge 822 may include a leading edge 830with a slant angle α and a trailing edge 840 with a slant angle β. Insome embodiments, leading edge 830 and training edge 840 of each ridge822 may be parallel to each other. In other words, slant angle α isapproximately equal to slant angle β. In some embodiments, slant angle αmay be different from slant angle β. In some embodiments, slant angle αmay be approximately equal to slant angle β. For example, the differencebetween slant angle α and slant angle β may be less than 20%, 10%, 5%,1%, or less. In some embodiments, slant angle α and slant angle β mayrange from, for example, about 30° or less to about 70° or larger. Insome embodiments, the slant angle α and/or slant angle β may be greaterthan 30°, 45°, 50°, 70°, or larger.

The slanted grating 820 may be fabricated using many differentnanofabrication techniques. The nanofabrication techniques generallyinclude a patterning process and a post-patterning (e.g., overcoating)process. The patterning process may be used to form slanted ridges 822of the slanted grating 820. There may be many different nanofabricationtechniques for forming the slanted ridges 822. For example, in someimplementations, the slanted grating 820 may be fabricated usinglithography techniques including slanted etching. In someimplementations, the slanted grating 820 may be fabricated usingnanoimprint lithography (NIL) from a master mold.

The post-patterning process may be used to overcoat the slanted ridges822 and/or to fill the grooves 824 between the slanted ridges 822 with amaterial having a refractive index n_(g2) different from the refractiveindex n_(g1) of the slanted ridges 822. The post-patterning process maybe independent from the patterning process. Thus, a same post-patterningprocess may be used on slanted gratings fabricated using any patteringtechnique.

FIG. 9A illustrates an example of a slanted grating coupler in awaveguide display 900 according to certain embodiments. The waveguidedisplay 900 may include slanted surface-relief structures, such asslanted gratings 920 on a substrate 910, such as a waveguide. Asdiscussed above and also shown in FIG. 9A, the configuration of theslanted gratings 920 may vary across the substrate 910 so as to increasethe coupling efficiency of the light to user's eyes. For example, someslanted gratings 920 a may include a period p₁ that may be differentfrom the period p₂ of other slanted gratings 920 b. The height of theridges 922 a and 922 b, the depth of the grooves 924 a and 924 b, andthe slant angles of the leading edges 930 a and 930 b and the trailingedges 940 a and 940 b of the ridges 922 a and 922 b may also vary. Thewidth of the ridges 922 a and 922 b and/or the width of the grooves 924a and 924 b may further be varied, leading to varied duty cycles of theslanted gratings 920 a and 920 b. The varied configuration of theslanted gratings 920 may pose challenges to overcoat the slantedgratings 920 uniformly and/or to form a substantially planar top surfaceof the overcoat layer.

Common techniques for applying an overcoat may include spin coatingtechniques. Generally, spin-coating techniques may work well to overcoata relatively flat surface. However, it may be challenging to achieve auniform overcoat layer when the surface to be coated may includestructures formed thereon, and it may be even more difficult to overcoatall exposed surfaces when the configuration of the surface structuresmay be varied across the surface, such as the varying configuration ofthe slanted gratings 920, or when some exposed surfaces may be shadowedby other surfaces and/or structures, such as trailing edges 940 and/orleading edges 930 of the slanted ridges 922. The resulting thickness ofan overcoat layer applied on the slanted gratings 920 using spin-coatingtechniques may vary, which can lead to an uneven or non-planar surfaceof the overcoat layer. The unevenness of the surface of the overcoatlayer can cause significant loss of coupled light. Further, solvent orair trapping may occur in the grooves 924 when spin-coating techniquesmay be employed. For example, the solvent used for spin coating theovercoat material may not completely evaporate. Air may also be trappedin the overcoat layer. The trapped solvent and/or air may result in avarying refractive index of the overcoat layer and efficiency loss ofthe device. The problems may be exacerbated when the grooves 924 may berelatively deep, e.g., 100 nm, 200 nm, 300 nm or greater in someembodiments, the grooves 924 may be relatively narrow, and/or the slantangles of the ridges 922 may be relatively large. In some embodiments,the slant angle may be greater than 30°, 45°, 50°, 70°, or larger.

To overcome these issues, different techniques for applying an overcoatover the slanted gratings 920 may be implemented. In some embodiments, acyclic coating or deposition process may be employed to fill the grooves924 and/or to overcoat the ridges 922. Specifically, instead of applyingan overcoat material to achieve a desired thickness of an overcoat layerall in once, the overcoat layer may be formed in multiple cycles, andduring each cycle, only a relatively thin layer of the overcoat materialmay be applied to partially fill the grooves 924 and/or to overcoat theridges 922. A desired thickness of the overcoat layer may be achievedthrough two or more cycles of the overcoat material application.

In some embodiments, the overcoat material may be applied or depositedusing atomic layer deposition (ALD) in each cycle. Specifically, oncethe slanted gratings 920 may be formed using any suitable techniques,the substrate 910 having the slanted gratings 920 formed thereon may betransferred to a processing chamber for application or deposition of theovercoat material. The slanted gratings 920 may be formed in the sameprocessing chamber in which the overcoat material may be applied ordeposited or may be formed in a different processing chamber. Theprocessing chamber may be configured to apply or deposit the overcoatmaterial in a cyclic manner. The processing chamber may be furtherconfigured to apply or deposit the overcoat material in a controlledamount during each cycle, including depositing the overcoat materialusing ALD in some embodiments. Accordingly, in some embodiments, only athin layer which may include two or more atomic layers of the overcoatmaterial may be deposited in each cycle. In some embodiments, only oneatomic layer of the overcoat material may be deposited in each cycle.The overcoat material may be deposited in a layer-by-layer fashion intwo or more cycles to achieve a desired overall thickness of theovercoat layer.

FIG. 9B illustrates the example slanted grating coupler of FIG. 9A thathas been coated with a layer of overcoat material according to certainembodiments. As illustrated, because the overcoat material may bedeposited in a layer-by-layer fashion, as the deposition progresses, thethickness of the overcoat material deposited on the top 950 of theridges 922 may be maintained to be substantially uniform. Further, whenperforming ALD, the pressure of the processing chamber may be maintainedrelatively low, such as close to vacuum. Under vacuum condition, themolecules forming the overcoat material may be adsorbed on all exposedsurfaces that may be oriented at any angle. Accordingly, duringdeposition of the overcoat material using ALD, the molecules forming theovercoat may not only be adsorbed on the top 950 of the ridges 922, butmay also be adsorbed on the surfaces of the leading edges 930 andtrailing edges 940 of the ridges 922, as well as the bottom 955 of thegrooves 924. Upon completion of one cycle, one continuous atomic layerof the overcoat material may be deposited or formed on the top 950 ofthe ridges 922, as well as inside the grooves 924 and on the leadingedges 930 and the trailing edges 940 of the ridges 922. As mentionedabove, it may be difficult to overcoat the leading edges 930 of theridges 922 partly because the leading edges 930, the trailing edges 940,and/or the bottom 955 of the grooves 924 may be shadowed by the ridges922. By using ALD, the molecules forming the overcoat material may beable to reach and to be uniformly adsorbed on the leading edges 930, thetrailing edges 940, and/or the bottom 955 of the grooves 924.Accordingly, a uniform overcoat may be obtained by using ALD even whenthe slant angles of the leading edges 930 and/or the trailing edges 940may be extremely high, such as greater than or about 30°, greater thanor about 35°, greater than or about 40°, greater than or about 45°,greater than or about 50°, greater than or about 55°, greater than orabout 60°, greater than or about 65°, greater than or about 70°, greaterthan or about 75°, greater than or about 80°, or greater.

As two or more cycles of the overcoat material application using ALD maybe performed, the thickness of the overcoat material deposited on thetop 950 of the ridges 922, the thickness of the overcoat materialdeposited on the leading edges 930 and the trailing edges 940 of theridges 922, and the thickness of the overcoat material deposited on thebottom 955 of the grooves 924 may grow or increase at substantially thesame or similar rate. Consequently, a substantially uniform thickness ofthe overcoat material on all exposed surfaces may be maintained duringthe deposition process, as illustrated in FIG. 9B, and the depositedovercoat material may reduce the depth of the grooves 924 and the widthof the grooves 924 simultaneously.

FIG. 9C illustrates the example slanted grating coupler of FIGS. 9A and9B that has been coated with additional overcoat material according tocertain embodiments. As shown, with more cycles of the deposition beingperformed, the uniformity in the thickness of the overcoat material onall exposed surfaces may be maintained during the deposition process.The depth of the grooves 924 and the width of the grooves 924 may befurther reduced simultaneously.

FIG. 9D illustrates the example slanted grating coupler of FIGS. 9A-9Cthat has been further coated with additional overcoat material to form aplanar overcoat layer according to certain embodiments. As shown, withfurther cycles of the deposition being performed, the gaps betweenadjacent ridges 922 may be eliminated, the grooves 924 may be completelyfilled by the overcoat material, and a continuous surface 960 of theovercoat layer may be formed by the overcoat material.

Because the overcoat material may be deposited in a layer-by-layerfashion, and in some embodiments, the top 950 of the individual slantedgratings 920 a and 920 b may be at the same height or elevation withrespect to a bottom surface of the substrate 910 as shown in FIG. 9A,the continuous surface 960 of the overcoat layer may be of the sameheight or elevation, and thus may be substantially flat or planar whenthe grooves 924 may be filled. In some embodiments, the surface 960 mayinclude no surface irregularities and thus is flat or planar. In someembodiments, the surface 960 may still include minor degree of surfaceirregularities, such as protrusions or dips. The depth of the dips orheight of the protrusions may be a few tens of nanometers to less than afew nanometers, may be less than 10 nm, less than 9 nm, less than 8 nm,less than 7 nm, less than 6 nm, less than 5 nm, less than 4 nm, lessthan 3 nm, less than 2 nm, less than 1 nm, less than 0.5 nm, or less invarious embodiments.

Depending on the applications, even when the surface 960 may includeminor degree of surface irregularities, the surface 960 may still beconsidered flat or planar, or substantially flat or planar. For example,in some embodiments, when the depth of the dips or height of theprotrusions may be less than 1% of the associated period p of theslanted gratings 920, the surface 960 may be considered flat or planar.Depending on the applications, the surface 960 may be considered flat orplanar when the depth of the dips or height of the protrusions may beless than 5% of the associated period p of the slanted gratings 920 insome embodiments, and may be considered flat or planar when the depth ofthe dips or height of the protrusions may be less than 4%, less than 3%,less than 2%, less than 1%, less than 0.5%, or less than 0.1% of theassociated period p of the slanted gratings 920 in various embodiments.

In some embodiments, one or more additional cycles of overcoat materialapplication may be performed to increase the thickness of the overcoatlayer. Because the surface 960 of the overcoat layer may besubstantially planar, the additional deposition may be performed usingALD or other physical and/or chemical techniques, including spin-coatingtechniques, to still maintain and achieve a substantially planar topsurface of the overcoat layer.

Although ALD is described herein as an exemplary technique for fillingthe grooves 924 of the slanted gratings 920, other depositiontechniques, such as other chemical vapor deposition (CVD) and/orphysical vapor deposition (PVD) techniques, may be utilized to depositthe overcoat material in a cyclic manner. During each cycle, only asmall amount of the materials forming the overcoat layer may be flowedinto the processing chamber to deposit a thin layer of the overcoatmaterial on the ridges 922 and inside the grooves 924. Consequently, thesurface profile of the deposited overcoat material layer may be improvedas compared to the surface profile obtained using conventionalspin-coating techniques. In some embodiments, the chamber componentsupporting the substrate 910 with the slanted gratings 920 formedthereon may be tilted so as to expose the grooves 924 to the incomingflow of the overcoat material to further facilitate uniform depositioninside the grooves 924.

As compared to applying the overcoat material all in once usingconventional spin-coating techniques, forming the overcoat layer in acyclic manner, whether using ALD or other CVD or PVD techniques, maygenerally improve the surface profile. Application of the overcoatmaterial using ALD may allow for even greater control over the surfaceprofile of the overcoat as compared to other CVD or PVD techniquesbecause only one atomic layer, i.e., about 0.5 nm thick, of the overcoatmaterial may be deposited during each cycle. Accordingly, the variationof the thickness deposited in each cycle may be less than 0.5 nm.Consequently, the variation of the overall thickness of the overcoat maybe extremely small, and may be within a few nanometers or less.

In addition to improved top surface uniformity, by depositing theovercoat material in a layer-by-layer fashion using ALD, a consistentrefractive index throughout the overcoat may also be achieved.Specifically, by using ALD to deposit the overcoat material inside thegrooves 924 layer by layer, the grooves 924 may be filled by theovercoat material with substantially no void. As discussed above,applying an overcoat using spin-coating techniques may result in solventor air trapping in the grooves 924, especially when the grooves 924 maybe relatively deep and/or narrow. The solvent or air trapped inside thegrooves 924 can lead to refractive index variation inside the overcoat,which can further lead to efficiency loss of the device. By applying theovercoat using ALD, no solvent may be introduced, and no air trappingmay occur, and thus, consistent and/or uniform refractive indexthroughout the overcoat may be obtained, which may further lead toimproved device efficiency.

The overcoat material may be substantially visibly transparent.Depending on the applications, the overcoat material may have arefractive index higher or lower than the refractive index of thematerial forming the ridges 922. In some embodiments, the materialforming the ridges 922 may include one of amorphous silicon, siliconoxide, silicon nitride, silicon carbide, silicon oxynitride (SiOxNy),spin on carbon (SOC), amorphous carbon, diamond like carbon (DLC),titanium oxide, aluminum oxide, tantalum oxide, or hafnium oxide. Insome embodiments, a high refractive index material, such as hafniumoxide, titanium oxide, tantalum oxide, tungsten oxide, zirconium oxide,gallium sulfide, gallium nitride, gallium phosphide, silicon, siliconnitride, and a high refractive index polymer, may be used to fill thegrooves 924. In some embodiments, a low refractive index material, suchas silicon oxide, alumina, porous silica, or fluorinated low indexmonomer (or polymer), may be used to fill the grooves 924. As a result,the difference between the refractive index of the ridges 922 and therefractive index of the grooves 924 filled with the overcoat materialmay be greater than 0.01, 0.05, 0.1, 0.2, 0.3, 0.5, 1.0, or higher. Theovercoat material and the ridges 922 may collectively function to couplelight into and out of the substrate 910.

FIG. 10 is a simplified flow chart 1000 illustrating an exemplary methodof applying an overcoat layer to a substrate according to certainembodiments. The operations described in flow chart 1000 are forillustration purposes only and are not intended to be limiting.

At block 1010, a substrate may be provided into a processing chamber.The substrate may include surface-relief structures similar to thosedescribed above with reference to FIGS. 8 and 9. Accordingly, thesubstrate may include slanted gratings having slanted ridges andgrooves. The configuration of the slanted ridges and grooves may varyacross the substrate as discussed above. The processing chamber for theovercoat layer application may be the same as or different from theprocessing chamber in which the slanted gratings may be formed.Accordingly, the substrate having the slanted gratings formed thereonmay be already in the processing chamber before block 1010.Alternatively, the substrate may be loaded into the processing chamberat block 1010 for application of the overcoat layer.

At block 1020, a layer of an overcoat material may be deposited onto thesubstrate to at least partially fill the grooves of the slantedgratings. In some embodiments, the processing chamber may be configuredto apply or deposit the overcoat material in a controlled amount. Thus,a thin layer of the overcoat material may be deposited at block 1020.Depending on the deposition techniques used and/or the operatingparameters of each technique, the thin layer of the overcoat materialmay include one atomic layer of the overcoat material in someembodiments, and may include a few atomic layers (i.e., two or moreatomic layers) of the overcoat material in some embodiments. When two ormore atomic layers of the overcoat material may be deposited, theoverall thickness of the overcoat material deposited may be controlledby determining or controlling the number of atomic layers of theovercoat material deposited and/or by determining or controlling thethickness of each overcoat material layer deposited at block 1020,depending on the deposition technique implemented.

In some embodiments, the processing chamber may be configured to depositthe overcoat material using ALD. Thus, one atomic layer of the overcoatmaterial may be deposited at block 1020. As discussed above, when ALDmay be implemented, the overcoat material may be evenly coated orapplied on all exposed surfaces, including surfaces that may be shadowedby other structures on the substrate. Consequently, depositing theovercoat material using ALD may achieve a substantially smooth or planartop surface of the overcoat layer, and improve the refractive indexconsistency throughout the overcoat layer. However, other depositiontechniques that may allow for thin-layer deposition, such as otherchemical vapor deposition (CVD) and/or physical vapor deposition (PVD)techniques, may also be implemented. In some embodiments, the chambercomponent configured to support the substrate may be tilted so as toexpose any shadowed surfaces, such as the surfaces defining thesidewalls and/or bottom of the grooves, to further facilitate evencoating or application of the overcoat material on all exposed surfaces.

At block 1030, it may be determined whether the grooves aresubstantially filled by the overcoat material. In some embodiments, theoperation at block 1030 may not be performed until several layers of theovercoat material have been deposited. In other words, the operation atblock 1030 may not be performed until the deposition operation at block1020 have been performed for multiple times or multiple cycles. Forexample, the number of layers of the overcoat material needed to fillthe grooves may be estimated such that the operation at block 1030 maybe performed after the deposition operation at block 1020 has beenrepeated for the estimated number of cycles or close to the estimatednumber of cycles. Depending on the applications, the grooves may beconsidered as being substantially filled by the overcoat material whenat least about 70%, at least about 75%, at least about 80%, at leastabout 85%, at least about 90%, at least about 91%, at least about 92%,at least about 93%, at least about 94%, at least about 95%, at leastabout 96%, at least about 97%, at least about 98%, at least about 99%,or about 100% of the depth of the grooves may be filled by the overcoatmaterial.

If at block 1030, it is determined that the grooves have not beensubstantially filled by the overcoat material, then the process mayproceed to block 1020 to deposit one or more additional layers of theovercoat material. The operations at block 1020 and block 1030 may berepeated until the grooves may be substantially filled by the overcoatmaterial. If at block 1030, it is determined that the grooves have beensubstantially filled by the overcoat material, then the method mayproceed to block 1040.

At block 1040, it may be determined whether a desired thickness of theovercoat layer has been achieved. In some embodiments, it may bedesirable to deposit the overcoat material to not only fill the groovesbut also to form an overcoat layer that has a thickness above the top ofthe ridges. Depending on the applications, the desired thickness of theovercoat layer above the top of the ridges may be greater than or about5% of the height of the ridges in some embodiments, and may be greaterthan or about 10%, greater than or about 15%, greater than or about 20%,greater than or about 25%, greater than or about 30%, greater than orabout 35%, greater than or about 40%, greater than or about 45%, greaterthan or about 50%, or greater percentage of the height of the ridges invarious embodiments. The height of a ridge may be defined as thedistance between the top of the ridge and the bottom of the adjacentgroove along the normal of the substrate on which the slanted gratingsmay be formed.

In some embodiments, substantially filling the grooves and depositing adesired thickness of the overcoat layer above the top of the ridges maybe achieved simultaneously. As discussed above with reference to FIGS.9A-9C, as the overcoat material may be deposited to fill the grooves,the overcoat material may also be deposited on the top of the ridges.When the grooves may be substantially filled by the overcoat material, acontinuous layer of the overcoat material may also be formed above thetop of ridges as shown in FIG. 9C. Accordingly, when it may bedetermined whether the grooves have been substantially filled, adetermination as to whether a desired thickness of the overcoat layermay be achieved may be performed at the same time. In other words, theoperation performed at block 1030 and the operation performed at block1040 may be performed simultaneously or may be performed in oneoperation.

If at block 1040, it is determined that the desired overcoat layerthickness above the top of the ridges has been achieved, then theprocess may proceed to block 1050, and the overcoat layer applicationmay be completed. Upon completion of the overcoat layer application, thesubstrate may be further processed in the same processing chamber or maybe removed from the processing chamber.

If at block 1040, it is determined that the desired overcoat layerthickness above the top of the ridges has not been achieved, then themethod may proceed to block 1060 to deposit additional overcoatmaterial. The additional overcoat material may be the same as ordifferent from the overcoat material applied at block 1020. If differentovercoat materials may be used at block 1020 and block 1060, the twodifferent overcoat materials may have matching refractive index. In someembodiments, the operation performed at block 1060 may be substantiallythe same as or similar to the operation performed at block 1020. Theovercoat material may be deposited using the same or similar depositiontechniques utilized at block 1020, including ALD or other PVD or CVDdeposition method. Thus, at block 1060, an additional layer of theovercoat material may be deposited, and the additional layer may be oneatomic layer of the overcoat material, or two or more atomic layers ofthe overcoat material, or a predetermined thickness of the overcoatmaterial deposited.

In some embodiments, the operation performed at block 1060 may bedifferent from the operation performed at block 1020. The operationperformed at block 1060 may use a different deposition technique and/ormay use different operating or deposition parameters for the samedeposition technique. Specifically, when the method may proceed to block1060, the grooves may be already substantially filled by the overcoatmaterial, and there may be substantially less variation in the surfaceprofile of the substrate as compared to the substrate with no overcoatmaterial. Accordingly, the overcoat material may be deposited at afaster deposition rate at block 1060 as compared to the deposition ratecontrolled at block 1020. Therefore, the deposition technique utilizedat block 1060 may include ALD to achieve a substantially planar topsurface of the overcoat layer in some embodiments. In some embodiments,the deposition technique utilized at block 1060 may include other PVD orCVD deposition techniques while still maintaining the surface evennessthat has been obtained through cycles of deposition operation performedat block 1020. In some embodiments, a spin-coating technique may even beutilized at block 1060. The issues with conventional spin-coatingtechniques, such as solvent or air trapping in the grooves and/orunevenness in the coating obtained, may be minimized or substantiallyavoided because of the significantly improved surface evenness obtainedafter cycles of deposition operation performed at block 1020. Operationsof block 1040 and block 1060 may be repeated in two or more cycles untilthe desired thickness of the overcoat layer above the top of the ridgesis obtained, and then the overcoat layer application may be completed atblock 1050.

With reference to FIG. 11, in some embodiments, surface variation, suchas dips 1170 may still be formed on the top surface 1160 of the overcoatmaterial upon completion of the cyclic deposition process, includingwhen the overcoat material may be deposited using ALD. The dips 1170 maybe formed partly due to the capability or limitation of the processingchamber, the deposition technique employed, and/or the variation in thestructure of the slanted gratings. Nonetheless, the dips 1170 may besignificantly shallower than those formed using conventionalspin-coating techniques. Further, depending on the specificapplications, the overcoat formed using the method described herein,even with the dips 1170 formed thereon, may still be within devicetolerance and thus can be used to couple light in and out of thewaveguide substrate. Further, the dips 1170 may be generally formedwhere the grooves are disposed or aligned with the grooves, and thus maybe formed at known locations and/or may appear periodically.Accordingly, the dips 1170 formed using the deposition method describedherein, including ALD as described herein, may be utilized as functionalstructures for light coupling and/or other purposes.

Depending on the techniques used, the depth D₁ of the dips 1170 mayvary. The depth D₁ of the dips 1170 may also vary depending on thestructure of the slanted gratings, such as the duty cycles of theslanted gratings, the width of the ridges and/or the grooves, the slantangles of the leading and trailing edges of the ridges, etc. Further,the corners of the ridges may be rounded in some embodiments, which mayalso affect the structure and/or depth of the dips 1170. A ratio of thedepth D₁ of the dips 1170 to the thickness D₂ of the overcoat materialbetween the top surface 1160 of the overcoat and the top 1150 of theridges may be less than or about 1:2, less than or about 1:3, less thanor about 1:4, less than or about 1:5, less than or about 1:6, less thanor about 1:7, less than or about 1:8, less than or about 1:9, less thanor about 1:10, less than or about 1:20, less than or about 1:30, lessthan or about 1:40, or less.

The thickness D₂ of the overcoat material over the top 1150 of theridges may depend on the period and/or duty cycle of the slantedgratings in some embodiments. For example, to overcoat slanted gratingswith a relatively large period and/or a relatively small duty cycle, theovercoat material over the top 1150 of the ridges may have a greaterthickness D₂ so as to form a continuous overcoat layer above the ridges.Conversely, to overcoat slanted gratings with a relatively small periodand/or a relatively large duty cycle, the overcoat material over the top1150 of the ridges may have a lesser thickness D₂ to form a continuousovercoat layer above the ridges. As discussed above, the period and/orthe duty cycle of the slanted gratings may vary across the substrate.The thickness D₂ of the overcoat material to be deposited over the top1150 may be determined based on the varying period and/or duty cyclesuch that a continuous overcoat layer may be formed over the slantedgratings across the entire substrate.

A ratio of the depth D₁ of the dips 1170 to the depth D₃ of the groovesas defined as the distance between the top 1150 of the adjacent ridgesand the bottom 1155 of the grooves may be less than or about 1:5, lessthan or about 1:6, less than or about 1:7, less than or about 1:8, lessthan or about 1:9, less than or about 1:10, less than or about 1:20,less than or about 1:30, less than or about 1:40, less than or about1:50, less than or about 1:60, or less. A ratio of the thickness D₂ ofthe overcoat material between the top surface 1160 of the overcoat andthe top 1150 of the ridges and the depth D₃ of the grooves may be lessthan or about 1:2, less than or about 1:3, less than or about 1:5, lessthan or about 1:10, less than or about 1:20, less than or about 1:30,less than or about 1:40, less than or about 1:50, less than or about1:60, less than or about 1:70, less than or about 1:80, less than orabout 1:90, less than or about 1:100, or less.

In some implementations, the depth D₃ of the grooves may be greater thanor about 100 nm, greater than or about 150 nm, greater than or about 200nm, greater than or about 250 nm, greater than or about 300 nm, orgreater. The thickness D₂ of the overcoat material between the topsurface 1160 of the overcoat and the top 1150 of the ridges may begreater than or about 10 nm, greater than or about 20 nm, greater thanor about 30 nm, greater than or about 40 nm, greater than or about 50nm, greater than or about 100 nm, greater than or about 150 nm, greaterthan or about 200 nm, or greater.

In some embodiments, the depth D₁ of the dips 1170 may be less than orabout 100 nm, less than or about 95 nm, less than or about 90 nm, lessthan or about 85 nm, less than or about 80 nm, less than or about 75 nm,less than or about 70 nm, less than or about 65 nm, less than or about60 nm, less than or about 55 nm, less than or about 50 nm, or less. Insome embodiments, the depth D₁ of the dips 1170 may be less than orabout 45 nm, less than or about 40 nm, less than or about 35 nm, lessthan or about 30 nm, less than or about 25 nm, less than or about 20 nm,less than or about 15 nm, less than or about 10 nm, less than or about 5nm, or less. In some embodiments, the depth D₁ of the dips 1170 may beabout 5 nm to 100 nm. In some embodiments, the depth D₁ of the dips 1170may be about 80 nm to 100 nm.

Depending on the applications, a substantially flat or planar topsurface of the overcoat, similar to the surface 960 shown in FIG. 9C,may be desired. Various processes may be implemented to limit or preventthe formation of the dips. In some embodiments, to limit dip formation,deposition and etching operations may be performed in each of multipleprocessing cycles.

FIG. 12 is a simplified flow chart 1200 illustrating an exemplary methodof applying an overcoat layer by performing deposition and etchingoperations in each of multiple processing cycles according to certainembodiments. The operations described in flow chart 1200 are forillustration purposes only and are not intended to be limiting. Theoperations of the method shown in FIG. 12 will be described inconjunction with the schematic illustration of FIGS. 13A-13D.

At block 1210, a substrate may be provided into a processing chamber.The substrate may include surface-relief structure similar to thosedescribed above with reference to FIGS. 8 and 9. Accordingly, thesubstrate may include slanted gratings having slanted ridges andgrooves. The configuration of the slanted ridges and grooves may varyacross the substrate as discussed above. The processing chamber for theovercoat layer application may be the same as or different from theprocessing chamber in which the slanted gratings may be formed.Accordingly, the substrate having the slanted gratings formed thereonmay be already in the processing chamber before block 1210.Alternatively, the substrate may be loaded into the processing chamberat block 1210 for application of the overcoat layer.

At block 1220, a thin layer of an overcoat material may be deposited inthe initial processing cycle on the exposed surfaces of the slantedgratings. The layer may be deposited using ALD or other suitabledeposition techniques described herein. For example, in someembodiments, other deposition techniques, such as other CVD and/or PVDtechniques may be employed. Although the other deposition techniques maynot achieve the same uniformity as an ALD process may achieve, thesubsequent etching operation performed during each processing cycle(described below) may reduce the non-uniformity, and may reduce theoverall depth of the dips that may be formed.

FIG. 13A illustrates an example slanted grating coupler that is coatedwith a layer 1310 of overcoat material according to certain embodiments.When ALD may be used, the thin layer 1310 may include at least about 5atomic layers of the overcoat material in some embodiments, and mayinclude at least about 10 atomic layers, at least about 20 atomiclayers, at least about 30 atomic layers, at least about 40 atomiclayers, at least about 50 atomic layers, or more atomic layers of theovercoat material in various embodiments. Alternatively, the overcoatmaterial may be deposited until the layer 1310 reaches a predeterminedthickness. For example, the overcoat material may be deposited until thelayer 1310 may be at least about 1 nm, at least about 2 nm, at leastabout 3 nm, at least about 4 nm, at least about 5 nm, at least about 10nm, at least about 15 nm, at least about 20 nm, at least about 25 nm, atleast about 30 nm, at least about 35 nm, at least about 40 nm, at leastabout 45 nm, at least about 50 nm, or greater in various embodiments.

At block 1230, an etching operation may be performed to remove at leastportions of the overcoat material deposited in the preceding depositionoperation. In some embodiments, the etching operation may be performedsuch that the overcoat material deposited on the top 1350 of the slantedgratings may be removed at a faster rate than the rate at which theovercoat material deposited inside the grooves 1324 may be removed.

FIG. 13B illustrates the example slanted grating coupler of FIG. 13A,where portions of the layer of overcoat material have been removedaccording to certain embodiments. In some embodiments, the operatingconditions of the etching operation may be controlled such thatsubstantially all of the overcoat material deposited on the top 1350 ofthe ridges 1322 may be removed while only a very limited amount of theovercoat material deposited inside the grooves 1324 may be removed. Forexample, the operating conditions may be controlled such thatanisotropic etching may be achieved. Anisotropic etching may be achievedby controlling the flow of the etchants. In some embodiments, theetchants may be flowed towards the slanted gratings in a directiongenerally perpendicular to the top 1350 of the ridges 1322. In someembodiments, the etchants may be flowed towards the trailing edges 1340of the ridges 1322 but away from the leading edges 1330 of the ridges1322. Consequently, the overcoat material deposited on the top 1350 ofthe ridges 1322 may be etched or removed, while the etching of theovercoat material deposited on the leading edges 1330 of the ridges 1322may be limited. The etching of the overcoat material deposited on thetrailing edges 1340 of the ridges 1322 may also be limited because theslanted orientation of the ridges 1322 may block or limit the etchantsthat may reach the trailing edge 1340 of an adjacent ridge 1322. Theslanted orientation of the ridges 1322 may also limit the amount of theovercoat material that may reach the bottom 1355 of the grooves 1324.Increasing the temperature and/or pressure of the processing chamber mayalso limit the amount of the etchants that may travel inside the grooves1324, resulting less of the overcoat material inside the grooves 1324being etched.

In some embodiments, the thickness of the overcoat material inside thegrooves 1324 that may be removed in an etching operation may be lessthan or about 50%, less than or about 40%, less than or about 30%, lessthan or about 20%, less than or about 10%, less than or about 5%, lessthan or about 3%, less than or about 2%, less than or about 1%, or lessof the thickness of the overcoat material deposited during the precedingdeposition operation. The thickness of the overcoat material on the top1350 of the ridges 1322 that may be removed in an etching operation maybe greater than or about 50%, greater than or about 60%, greater than orabout 70%, greater than or about 80%, greater than or about 90%, greaterthan or about 95%, or about 100% of the thickness of the overcoatmaterial deposited during the preceding deposition operation.

At block 1240, it may be determined whether the grooves aresubstantially filled by the overcoat material. In some embodiments,operation at block 1240 may not be performed until several cycles of thedeposition and etching operations have been performed. Depending on theapplications, the grooves may be considered as being substantiallyfilled by the overcoat material when at least about 70%, at least about75%, at least about 80%, at least about 85%, at least about 90%, atleast about 91%, at least about 92%, at least about 93%, at least about94%, at least about 95%, at least about 96%, at least about 97%, atleast about 98%, at least about 99%, or about 100% of the depth of thegrooves may be filled by the overcoat material. If at block 1240, it isdetermined that the grooves have not been substantially filled by theovercoat material, then the process may proceed to block 1210 to depositanother layer of the overcoat material, followed by another etchingoperation at block 1230.

In some embodiments, the amount of the overcoat material depositedduring the deposition operation may remain the same from cycle to cycle,and the amount of the overcoat material removed during the etchingoperation may also remain the same from cycle to cycle. In someembodiments, at least one or both of the amount of the overcoat materialdeposited and/or the amount of the overcoat material removed may varyfrom cycle to cycle. In some embodiments, the duration of the depositionoperation may remain the same from cycle to cycle, and the duration ofthe etching operation may also remain the same from cycle to cycle. Insome embodiments, at least one or both of the duration of the depositionand/or the duration of the etching operations may vary from cycle tocycle.

FIG. 13C illustrates the example slanted grating coupler of FIGS. 13Aand 13B that has been coated with additional overcoat material accordingto certain embodiments. By repeating the deposition operation andetching operation in multiple processing cycles, the grooves 1324 may begradually filled up by the overcoat material while the overcoat materialmay not build up on the top 1350 of the ridges 1322, resulting in astructure similar to that shown in FIG. 13C. As shown in FIG. 13C, byimplementing a cyclic process where each cycle may include a depositionoperation followed by an etching operation, when the grooves 1324 may besubstantially filled by the overcoat material, the top 1350 of theridges 1322 and the top 1380 of the overcoat material filling eachgroove 1324 may collectively form a substantially flat or even topsurface. The depth of the dips or other surface irregularities that maybe formed by the overcoat material may be less than 1% of the period pof the slanted gratings in some embodiments, and may be less than 0.9%,less than 0.7%, less than 0.5%, less than 0.3%, or less than 0.1% of theperiod p of the slanted gratings in various embodiments. Depending onthe configuration of the gratings, the depth of the dips or othersurface irregularities may be less than 5 nm, less than 4 nm, less than3 nm, less than 2 nm, less than 1 nm, less than 0.5 nm, or less invarious embodiments.

Once the grooves have been substantially filled by the overcoatmaterial, the method may proceed to block 1250 to deposit additionalovercoat material until a desired thickness of the overcoat layer abovethe top 1350 of the ridges 1322 may be achieved. The additional overcoatmaterial may be the same as or different from the overcoat materialapplied at block 1220. If different overcoat materials may be used atblock 1220 and block 1240, the two different overcoat materials may havematching refractive index. In some embodiments, the additional overcoatmaterial may be deposited using the same or similar depositiontechniques utilized at block 1220, including ALD or other PVD or CVDdeposition method. In some embodiments, the additional overcoat materialmay be applied using a spin-coating technique because the top 1350 ofthe ridges 1322 and the top 1380 of the overcoat material filling eachgroove 1324 may be substantially level as shown in FIG. 13C.

FIG. 13D illustrates the example slanted grating coupler with of FIGS.13A-13C that has been further coated with additional overcoat materialto form a planar overcoat layer according to certain embodiments. Asillustrated, upon completion the deposition of the additional overcoatmaterial, a substantially flat or planar top surface 1360 of theovercoat layer, similar to that shown in FIG. 9C, may be achieved withsubstantially no dips formed. If any dips or other surfaceirregularities may be formed, depending on the techniques used to applythe additional overcoat material, the dimension of the surfaceirregularities may be less than 1%, less than 0.9%, less than 0.7%, lessthan 0.5%, less than 0.3%, or less than 0.1% of the period p of theslanted gratings in various embodiments, and/or may be less than 5 nm,less than 4 nm, less than 3 nm, less than 2 nm, less than 1 nm, lessthan 0.5 nm, or less in various embodiments.

FIG. 14 is a simplified flow chart 1400 illustrating an exemplaryplanarization process that may improve the surface finishing of anovercoat layer according to certain embodiments. The operationsdescribed in flow chart 1400 are for illustration purposes only and arenot intended to be limiting. The operations of the method shown in FIG.14 will be described in conjunction with the schematic illustration ofFIGS. 15A-15D.

At block 1410, a substrate may be provided into a processing chamber.The substrate may include surface-relief structures similar to thosedescribed above with reference to FIGS. 8 and 9. The substrate mayfurther include an overcoat layer deposited over the substrate using ALDor other deposition techniques described herein. As shown in FIG. 15A,the overcoat material deposited may include dips 1570 formed on the topsurface, similar to those described above with reference to FIG. 11.Each dip 1570 may be defined by a concave surface portion of theovercoat material having two opposing sloped sides, a first sloped side1510 and a second sloped side 1520, and a bottom 1515 between the firstand second sloped sides 1510 and 1520. Depending on the depositiontechniques employed, the surface portions 1580 between the dips 1570 maybe substantially flat or planar in some embodiments. To reduce the depthof the dips 1570 or to remove the dips 1570 entirely, ion beam etchingmay be utilized.

Although dips formed on the top surface of an overcoat layer aredescribed herein as exemplary surface irregularities, the methods and/orplanarization techniques described herein are not intended to be limitedto removing dips on the surface of the overcoat only. The methods and/orplanarization techniques described herein can be utilized to reduce orremove other surface irregularities on any other surfaces formed usingany deposition, coating, growth, or other forming processes. The surfaceirregularities may be concave, convex, recessed, protruding, and/or mayappear periodically or non-periodically.

At block 1420, a glancing ion bean etching may be performed to reducethe depth of the dips 1170. Specifically, with reference to FIG. 15B, anion beam 1590 may be oriented such that the angle between the incidention beam 1590 and the surface portions 1580 may be relatively small. Insome embodiments, the ion beam 1590 may be nearly parallel to thesubstantially planar surface portions 1580 in some embodiments.Accordingly, the ion beam 1590 may also be referred to as a glancing ionbeam 1590, and the etching performed by the glancing ion beam may bereferred to as a glancing ion beam etching.

In some embodiments, the ion beam 1590 may be oriented or angled withrespect to the surface portions 1580 and/or the top 1550 of the ridgesin a manner such that one sloped side 1510 or 1520 of each dip 1570 maybe reached or bombarded by the incident ion beam 1590 while the othersloped side 1510 or 1520 and the bottom 1515 of each dip 1570 may not bereached or bombarded by the ion beam 1590. For example, in theembodiment shown in FIG. 15B, the angle between the incident ion beam1590 and the surface portions 1580, or the glancing angle of the ionbeam 1590, may be less than or about the angle θ₁ between the firstsloped surfaces 1510 of the dips 1570 and the adjacent surface portions1580. Consequently, the ion beam 1590 may reach the surface portions1580 and the second slope side 1520 of each dip 1570. The ion beam 1590may not reach the first sloped side 1510 and the bottom 1515 of each dip1570 because the adjacent surface portion 1580 may block the ion beam1590, or stated differently, the first sloped side 1510 and/or thebottom 1515 may be shadowed by the surface portions 1580. By orientingthe incident ion beam 1590 in this manner, the depth of the dips 1570may not be increased by the ion beam 1590. Instead, the depth of thedips 1570 may be reduced as compared to those shown in FIG. 15A, becausethe overcoat material forming the surface portions 1580 and the secondsloped side 1520 of each dip 1570 may be removed by the ion beam 1590.Similarly, although the first sloped side 1510 of each dip 1570 may notbe bombarded by the ion beam 1590, the first sloped sides 1510 of thedips 1570 may also gradually decrease because of the removal or etchingof the adjacent surface portions 1580.

Similarly, when the ion beam 1590 may be directed towards the slantedgratings 920 from the opposite side, the ion beam 1590 may be orientedsuch that the glancing angle of the ion beam 1590 may be less than orabout the angle θ₂ between the second sloped sides 1520 of the dips 1570and the adjacent surface portions 1580. With such configuration, theovercoat material forming the surface portions 1580 and the first slopedsides 1510 of the dips 1570 may be removed by the ion beam 1590 withoutincreasing the depth of the dips 1570. The dips 1570 may becomeshallower, and eventually may be completely eliminated as the ion beametching progresses to form a substantially planar top surface of theovercoat.

At block 1430, it may be determined whether a desired surface evennesshas been achieved. Depending on the applications, a desired surfaceevenness may be substantially planar by complete removal of all dips1170 or other surface irregularities formed in some embodiments. In someembodiments, certain surface evenness may be tolerated. For example, itmay be determined that a desired surface evenness has been achieved whenthe depth of the dips 1170 or other concave surface irregularities orthe height of convex or protruding surface irregularities may be reducedto less than or about 100 nm, less than or about 90 nm, less than orabout 85 nm, less than or about 80 nm, less than or about 75 nm, lessthan or about 70 nm, less than or about 65 nm, less than or about 60 nm,less than or about 55 nm, less than or about 50 nm, less than or about45 nm, less than or about 40 nm, less than or about 35 nm, less than orabout 30 nm, less than or about 25 nm, less than or about 20 nm, lessthan or about 15 nm, less than or about 10 nm, less than or about 9 nm,less than or about 8 nm, less than or about 7 nm, less than or about 6nm, less than or about 5 nm, less than or about 4 nm, less than or about3 nm, less than or about 2 nm, less than or about 1 nm, less than orabout 0.5 nm, or less.

If it is determined at block 1430 that the desired surface evenness hasbeen achieved, then the planarization process may be completed at bock1450. If it is determined at block 1430 that the desired surfaceevenness has not been achieved, the process may proceed to block 1420 tocontinue etching the overcoat layer with the glancing ion beam until thedesired surface evenness is achieved.

At block 1440, in some embodiments, when it is determined that continuedetching may be performed, the process may include gradually decreasingthe glancing angle of the ion beam 1590 as the dips 1570 may becomeshallower and shallower, such as shown in FIG. 15C. The initial glancingangle of the ion beam 1590 may be about 15° or greater. The glancingangle of the ion beam 1590 may be gradually reduced toward 0°. In someembodiments, the glancing angle of the ion beam 1590 may be reduced fromabout 15° to about 1° or to 0° as the ion beam etching progresses.

In some embodiments, to increase the etch rate or shorten the etchingtime by the ion beam 1590, the angle between the ion beam 1590 and thefirst sloped side 1510 in the embodiment shown in FIG. 15B or the anglebetween the ion beam 1590 and the second sloped side 1520 in otherembodiments may be about or slightly greater than θ₁ or θ₂,respectively. In these embodiments, although both sloped sides 1510 and1520 may be etched by the ion beam 1590, one of the sloped sides 1510and 1520 may be etched at a rate that may be significantly greater thanthe rate at which the other sloped side 1510 or 1520 may etched. As theangle between the ion beam 1590 and the surface portions 1580 maygradually decrease, the etching of the other sloped side 1510 or 1520may be completely stopped.

As planarization process progresses, the dips 1570 or other surfaceirregularities may be completely removed, and a substantially flat orplanar surface 1585 of the overcoat material, as shown in FIG. 15D, maybe obtained. If any surface irregularities may remain, the dimension ofthe remaining surface irregularities may be less than 1%, less than0.9%, less than 0.7%, less than 0.5%, less than 0.3%, or less than 0.1%of the period p of the slanted gratings, and/or less than 5 nm, lessthan 4 nm, less than or about 3 nm, less than or about 2 nm, less thanor about 1 nm, less than or about 0.5 nm, or less in variousembodiments.

Although ion beam etching is described herein as an example, otheretching or planarization techniques may be utilized. In someembodiments, chemical-mechanical planarization technique may be used toimprove the surface profile and/or to obtain a substantially planar orflat top surface of the overcoat.

FIG. 16A is a simplified flow chart 1600A illustrating an exemplaryplanarization process that may improve the surface finishing of anovercoat layer according to certain embodiments. The operationsdescribed in flow chart 1600A are for illustration purposes only and arenot intended to be limiting. The operations of the method shown in FIG.16A will be described in conjunction with the schematic illustration ofFIGS. 17A and 17B.

At block 1610 a, a substrate may be provided. The substrate may includesurface-relief structure similar to those described above with referenceto FIGS. 8 and 9. The substrate may further include a first overcoatlayer 1710 deposited over the substrate as shown in FIG. 17A. The firstovercoat layer 1710 may include dips 1770 formed on the top surface,similar to those described above with reference to FIG. 11. The firstovercoat layer 1710 may be deposited using ALD or other cyclicdeposition techniques described herein.

At block 1620 a, a second overcoat layer 1720 may be deposited using aspin-coating operation. As discussed above, when a cyclic depositionprocess may be implemented, in particular when ALD may be employed, theevenness of the top surface of the overcoat material so deposited may besignificantly improved as compared to a non-coated substrate withvarying surface-relief structures formed thereon. As such, thespin-coating operation may be performed following the depositionoperation to obtain a substantially uniform overcoat layer 1720 as shownin FIG. 17B, and the top surface 1730 of the second overcoat layer 1720may be substantially planar. If any surface irregularities may bepresent, the dimension of the surface irregularities may be less than1%, less than 0.9%, less than 0.7%, less than 0.5%, less than 0.3%, orless than 0.1% of the period p of the slanted gratings, and/or may beless than 5 nm, less than 4 nm, less than 3 nm, less than 2 nm, lessthan 1 nm, less than 0.5 nm, or less in various embodiments.

In some embodiments, the material forming the first overcoat layer 1710and the material forming the second overcoat layer 1720 may be the same.In some embodiments, although the material forming the second overcoatlayer 1720 may be different from the material forming the first overcoatlayer 1710, the materials may have matching refractive index. If therefractive index of the first overcoat layer 1710 matches the refractiveindex of the second overcoat layer 1720, the planarization process maybe completed after depositing the second overcoat layer 1720.

FIG. 16B is a simplified flow chart 1600B illustrating an exemplaryplanarization process that may improve the surface finishing of anovercoat layer according to certain embodiments. The operationsdescribed in flow chart 1600B are for illustration purposes only and arenot intended to be limiting. The operations of the method shown in FIG.16B will be described in conjunction with the schematic illustration ofFIGS. 18A-18D.

Operations performed at block 1610 b and block 1620 b may be similar tothose performed at blocks 1610 a and 1620 a, respectively. Specifically,at block 1610 b, a substrate having a surface-relief structure coveredby a first overcoat layer 1810 as shown in FIG. 18A may be provided. Thefirst overcoat layer 1810 may include dips 1870 formed on the topsurface of the first overcoat layer 1810. At block 1620 b, a secondovercoat layer 1820 may be deposited using a spin-coating operation asshown in FIG. 18B. Similar to the top surface 1730 of the secondovercoat layer 1720 shown in FIG. 17B, the top surface 1830 of thesecond overcoat layer 1820 may be substantially planar due to theimproved surface evenness in the first overcoat layer 1810 obtained byusing ALD or other cyclic deposition methods described herein.

At block 1630 b, an etching operation may be performed to remove theentire second overcoat layer 1820 and to remove portions of the firstovercoat layer 1810. In this embodiment, the refractive index of thematerial forming the second overcoat layer 1820 and the refractive indexof the material forming the first overcoat layer 1810 may not match. Thedifference may be due to different materials used for forming the firstand second overcoat layers 1810 and 1820 and/or differentdeposition/formation processes implemented. However, the materialforming the second overcoat layer 1820 may be selected such that thematerial forming the second overcoat layer 1820 and the material formingthe first overcoat layer 1810 may be etched at substantially the samerate. Accordingly, by performing a subsequent etching operation at block1630 b, such as a dry etching process that may have about 1:1 etchselectivity toward both materials or etch both materials at the samerate, the flatness or evenness of the top surface of the overcoat layermay be maintained during the etching process.

Specifically, as shown in FIG. 18C, when the second overcoat layer 1820may be etched away to expose portions of the first overcoat layer 1810,due to the 1:1 selectivity, the etching operation may continue etch theremaining second overcoat layer 1820 and the exposed portions of thefirst overcoat layer 1810 at the same rate, and thus may maintain aflatness or evenness of the top surface of the overcoat layer.

Upon completion of the planarization process, a substantially flat orplanar top surface of the first overcoat layer 1810 of the overcoat maybe achieved as shown in FIG. 18D. The dimension of any surfaceirregularities that may be present may be less than 1%, less than 0.9%,less than 0.7%, less than 0.5%, less than 0.3%, or less than 0.1% of theperiod p of the slanted gratings, and/or may be less than 5 nm, lessthan 4 nm, less than 3 nm, less than 2 nm, less than 1 nm, less than 0.5nm, or less in various embodiments, partly depending on the etchingtechniques utilized. Although a dry etching process is described as anexample, the second overcoat layer 1820 and/or the first overcoat layer1810 may be removed using other removal process, such as achemical-mechanical planarization process, ion beam etching, includingthe glancing ion beam etching described herein, or other suitableetching or removal techniques.

The various technologies described herein allow for integration ofextreme slant structures with an overcoat layer and flexibility inselecting the refractive index of the overcoat material. Thetechnologies described herein can minimize thickness variation, and asubstantially planar top surface of the overcoat may be obtained. Thetechnologies described herein may also reduce or eliminate verticalrefractive index variation of the overcoat layer.

Embodiments of the invention may include or be implemented inconjunction with an artificial reality system. Artificial reality is aform of reality that has been adjusted in some manner beforepresentation to a user, which may include, e.g., a virtual reality (VR),an augmented reality (AR), a mixed reality (MR), a hybrid reality, orsome combination and/or derivatives thereof. Artificial reality contentmay include completely generated content or generated content combinedwith captured (e.g., real-world) content. The artificial reality contentmay include video, audio, haptic feedback, or some combination thereof,and any of which may be presented in a single channel or in multiplechannels (such as stereo video that produces a three-dimensional effectto the viewer). Additionally, in some embodiments, artificial realitymay also be associated with applications, products, accessories,services, or some combination thereof, that are used to, e.g., createcontent in an artificial reality and/or are otherwise used in (e.g.,perform activities in) an artificial reality. The artificial realitysystem that provides the artificial reality content may be implementedon various platforms, including a head-mounted display (HMD) connectedto a host computer system, a standalone HMD, a mobile device orcomputing system, or any other hardware platform capable of providingartificial reality content to one or more viewers.

FIG. 19 is a simplified block diagram of an example electronic system1900 of an example near-eye display (e.g., HMD device) for implementingsome of the examples disclosed herein. Electronic system 1900 may beused as the electronic system of an HMD device or other near-eyedisplays described above. In this example, electronic system 1900 mayinclude one or more processor(s) 1910 and a memory 1920. Processor(s)1910 may be configured to execute instructions for performing operationsat a number of components, and can be, for example, a general-purposeprocessor or microprocessor suitable for implementation within aportable electronic device. Processor(s) 1910 may be communicativelycoupled with a plurality of components within electronic system 1900. Torealize this communicative coupling, processor(s) 1910 may communicatewith the other illustrated components across a bus 1940. Bus 1940 may beany subsystem adapted to transfer data within electronic system 1900.Bus 1940 may include a plurality of computer buses and additionalcircuitry to transfer data.

Memory 1920 may be coupled to processor(s) 1910. In some embodiments,memory 1920 may offer both short-term and long-term storage and may bedivided into several units. Memory 1920 may be volatile, such as staticrandom access memory (SRAM) and/or dynamic random access memory (DRAM)and/or non-volatile, such as read-only memory (ROM), flash memory, andthe like. Furthermore, memory 1920 may include removable storagedevices, such as secure digital (SD) cards. Memory 1920 may providestorage of computer-readable instructions, data structures, programmodules, and other data for electronic system 1900. In some embodiments,memory 1920 may be distributed into different hardware modules. A set ofinstructions and/or code might be stored on memory 1920. Theinstructions might take the form of executable code that may beexecutable by electronic system 1900, and/or might take the form ofsource and/or installable code, which, upon compilation and/orinstallation on electronic system 1900 (e.g., using any of a variety ofgenerally available compilers, installation programs,compression/decompression utilities, etc.), may take the form ofexecutable code.

In some embodiments, memory 1920 may store a plurality of applicationmodules 1922 through 1924, which may include any number of applications.Examples of applications may include gaming applications, conferencingapplications, video playback applications, or other suitableapplications. The applications may include a depth sensing function oreye tracking function. Application modules 1922-1924 may includeparticular instructions to be executed by processor(s) 1910. In someembodiments, certain applications or parts of application modules1922-1924 may be executable by other hardware modules 1980. In certainembodiments, memory 1920 may additionally include secure memory, whichmay include additional security controls to prevent copying or otherunauthorized access to secure information.

In some embodiments, memory 1920 may include an operating system 1925loaded therein. Operating system 1925 may be operable to initiate theexecution of the instructions provided by application modules 1922-1924and/or manage other hardware modules 1980 as well as interfaces with awireless communication subsystem 1930 which may include one or morewireless transceivers. Operating system 1925 may be adapted to performother operations across the components of electronic system 1900including threading, resource management, data storage control and othersimilar functionality.

Wireless communication subsystem 1930 may include, for example, aninfrared communication device, a wireless communication device and/orchipset (such as a Bluetooth® device, an IEEE 802.11 device, a Wi-Fidevice, a WiMax device, cellular communication facilities, etc.), and/orsimilar communication interfaces. Electronic system 1900 may include oneor more antennas 1934 for wireless communication as part of wirelesscommunication subsystem 1930 or as a separate component coupled to anyportion of the system. Depending on desired functionality, wirelesscommunication subsystem 1930 may include separate transceivers tocommunicate with base transceiver stations and other wireless devicesand access points, which may include communicating with different datanetworks and/or network types, such as wireless wide-area networks(WWANs), wireless local area networks (WLANs), or wireless personal areanetworks (WPANs). A WWAN may be, for example, a WiMax (IEEE 802.16)network. A WLAN may be, for example, an IEEE 802.11x network. A WPAN maybe, for example, a Bluetooth network, an IEEE 802.15x, or some othertypes of network. The techniques described herein may also be used forany combination of WWAN, WLAN, and/or WPAN. Wireless communicationssubsystem 1930 may permit data to be exchanged with a network, othercomputer systems, and/or any other devices described herein. Wirelesscommunication subsystem 1930 may include a means for transmitting orreceiving data, such as identifiers of HMD devices, position data, ageographic map, a heat map, photos, or videos, using antenna(s) 1934 andwireless link(s) 1932. Wireless communication subsystem 1930,processor(s) 1910, and memory 1920 may together comprise at least a partof one or more of a means for performing some functions disclosedherein.

Embodiments of electronic system 1900 may also include one or moresensors 1990. Sensor(s) 1990 may include, for example, an image sensor,an accelerometer, a pressure sensor, a temperature sensor, a proximitysensor, a magnetometer, a gyroscope, an inertial sensor (e.g., a modulethat combines an accelerometer and a gyroscope), an ambient lightsensor, or any other similar module operable to provide sensory outputand/or receive sensory input, such as a depth sensor or a positionsensor. For example, in some implementations, sensor(s) 1990 may includeone or more inertial measurement units (IMUs) and/or one or moreposition sensors. An IMU may generate calibration data indicating anestimated position of the HMD device relative to an initial position ofthe HMD device, based on measurement signals received from one or moreof the position sensors. A position sensor may generate one or moremeasurement signals in response to motion of the HMD device. Examples ofthe position sensors may include, but are not limited to, one or moreaccelerometers, one or more gyroscopes, one or more magnetometers,another suitable type of sensor that detects motion, a type of sensorused for error correction of the IMU, or some combination thereof. Theposition sensors may be located external to the IMU, internal to theIMU, or some combination thereof. At least some sensors may use astructured light pattern for sensing.

Electronic system 1900 may include a display module 1960. Display module1960 may be a near-eye display, and may graphically present information,such as images, videos, and various instructions, from electronic system1900 to a user. Such information may be derived from one or moreapplication modules 1922-1924, virtual reality engine 1926, one or moreother hardware modules 1980, a combination thereof, or any othersuitable means for resolving graphical content for the user (e.g., byoperating system 1925). Display module 1960 may use liquid crystaldisplay (LCD) technology, light-emitting diode (LED) technology(including, for example, OLED, ILED, mLED, AMOLED, TOLED, etc.), lightemitting polymer display (LPD) technology, or some other displaytechnology.

Electronic system 1900 may include a user input/output module 1970. Userinput/output module 1970 may allow a user to send action requests toelectronic system 1900. An action request may be a request to perform aparticular action. For example, an action request may be to start or endan application or to perform a particular action within the application.User input/output module 1970 may include one or more input devices.Example input devices may include a touchscreen, a touch pad,microphone(s), button(s), dial(s), switch(es), a keyboard, a mouse, agame controller, or any other suitable device for receiving actionrequests and communicating the received action requests to electronicsystem 1900. In some embodiments, user input/output module 1970 mayprovide haptic feedback to the user in accordance with instructionsreceived from electronic system 1900. For example, the haptic feedbackmay be provided when an action request is received or has beenperformed.

Electronic system 1900 may include a camera 1950 that may be used totake photos or videos of a user, for example, for tracking the user'seye position. Camera 1950 may also be used to take photos or videos ofthe environment, for example, for VR, AR, or MR applications. Camera1950 may include, for example, a complementary metal-oxide-semiconductor(CMOS) image sensor with a few millions or tens of millions of pixels.In some implementations, camera 1950 may include two or more camerasthat may be used to capture 3-D images.

In some embodiments, electronic system 1900 may include a plurality ofother hardware modules 1980. Each of other hardware modules 1980 may bea physical module within electronic system 1900. While each of otherhardware modules 1980 may be permanently configured as a structure, someof other hardware modules 1980 may be temporarily configured to performspecific functions or temporarily activated. Examples of other hardwaremodules 1980 may include, for example, an audio output and/or inputmodule (e.g., a microphone or speaker), a near field communication (NFC)module, a rechargeable battery, a battery management system, awired/wireless battery charging system, etc. In some embodiments, one ormore functions of other hardware modules 1980 may be implemented insoftware.

In some embodiments, memory 1920 of electronic system 1900 may alsostore a virtual reality engine 1926. Virtual reality engine 1926 mayexecute applications within electronic system 1900 and receive positioninformation, acceleration information, velocity information, predictedfuture positions, or some combination thereof of the HMD device from thevarious sensors. In some embodiments, the information received byvirtual reality engine 1926 may be used for producing a signal (e.g.,display instructions) to display module 1960. For example, if thereceived information indicates that the user has looked to the left,virtual reality engine 1926 may generate content for the HMD device thatmirrors the user's movement in a virtual environment. Additionally,virtual reality engine 1926 may perform an action within an applicationin response to an action request received from user input/output module1970 and provide feedback to the user. The provided feedback may bevisual, audible, or haptic feedback. In some implementations,processor(s) 1910 may include one or more GPUs that may execute virtualreality engine 1926.

In various implementations, the above-described hardware and modules maybe implemented on a single device or on multiple devices that cancommunicate with one another using wired or wireless connections. Forexample, in some implementations, some components or modules, such asGPUs, virtual reality engine 1926, and applications (e.g., trackingapplication), may be implemented on a console separate from thehead-mounted display device. In some implementations, one console may beconnected to or support more than one HMD.

In alternative configurations, different and/or additional componentsmay be included in electronic system 1900. Similarly, functionality ofone or more of the components can be distributed among the components ina manner different from the manner described above. For example, in someembodiments, electronic system 1900 may be modified to include othersystem environments, such as an AR system environment and/or an MRenvironment.

The methods, systems, and devices discussed above are examples. Variousembodiments may omit, substitute, or add various procedures orcomponents as appropriate. For instance, in alternative configurations,the methods described may be performed in an order different from thatdescribed, and/or various stages may be added, omitted, and/or combined.Also, features described with respect to certain embodiments may becombined in various other embodiments. Different aspects and elements ofthe embodiments may be combined in a similar manner. Also, technologyevolves and, thus, many of the elements are examples that do not limitthe scope of the disclosure to those specific examples.

Specific details are given in the description to provide a thoroughunderstanding of the embodiments. However, embodiments may be practicedwithout these specific details. For example, well-known circuits,processes, systems, structures, and techniques have been shown withoutunnecessary detail in order to avoid obscuring the embodiments. Thisdescription provides example embodiments only, and is not intended tolimit the scope, applicability, or configuration of the invention.Rather, the preceding description of the embodiments will provide thoseskilled in the art with an enabling description for implementing variousembodiments. Various changes may be made in the function and arrangementof elements without departing from the spirit and scope of the presentdisclosure.

Also, some embodiments were described as processes depicted as flowdiagrams or block diagrams. Although each may describe the operations asa sequential process, many of the operations may be performed inparallel or concurrently. In addition, the order of the operations maybe rearranged. A process may have additional steps not included in thefigure. Furthermore, embodiments of the methods may be implemented byhardware, software, firmware, middleware, microcode, hardwaredescription languages, or any combination thereof. When implemented insoftware, firmware, middleware, or microcode, the program code or codesegments to perform the associated tasks may be stored in acomputer-readable medium such as a storage medium. Processors mayperform the associated tasks.

It will be apparent to those skilled in the art that substantialvariations may be made in accordance with specific requirements. Forexample, customized or special-purpose hardware might also be used,and/or particular elements might be implemented in hardware, software(including portable software, such as applets, etc.), or both. Further,connection to other computing devices such as network input/outputdevices may be employed.

With reference to the appended figures, components that can includememory can include non-transitory machine-readable media. The term“machine-readable medium” and “computer-readable medium” may refer toany storage medium that participates in providing data that causes amachine to operate in a specific fashion. In embodiments providedhereinabove, various machine-readable media might be involved inproviding instructions/code to processing units and/or other device(s)for execution. Additionally or alternatively, the machine-readable mediamight be used to store and/or carry such instructions/code. In manyimplementations, a computer-readable medium is a physical and/ortangible storage medium. Such a medium may take many forms, including,but not limited to, non-volatile media, volatile media, and transmissionmedia. Common forms of computer-readable media include, for example,magnetic and/or optical media such as compact disk (CD) or digitalversatile disk (DVD), punch cards, paper tape, any other physical mediumwith patterns of holes, a RAM, a programmable read-only memory (PROM),an erasable programmable read-only memory (EPROM), a FLASH-EPROM, anyother memory chip or cartridge, a carrier wave as described hereinafter,or any other medium from which a computer can read instructions and/orcode. A computer program product may include code and/ormachine-executable instructions that may represent a procedure, afunction, a subprogram, a program, a routine, an application (App), asubroutine, a module, a software package, a class, or any combination ofinstructions, data structures, or program statements.

Those of skill in the art will appreciate that information and signalsused to communicate the messages described herein may be representedusing any of a variety of different technologies and techniques. Forexample, data, instructions, commands, information, signals, bits,symbols, and chips that may be referenced throughout the abovedescription may be represented by voltages, currents, electromagneticwaves, magnetic fields or particles, optical fields or particles, or anycombination thereof.

Terms, “and” and “or” as used herein, may include a variety of meaningsthat are also expected to depend at least in part upon the context inwhich such terms are used. Typically, “or” if used to associate a list,such as A, B, or C, is intended to mean A, B, and C, here used in theinclusive sense, as well as A, B, or C, here used in the exclusivesense. In addition, the term “one or more” as used herein may be used todescribe any feature, structure, or characteristic in the singular ormay be used to describe some combination of features, structures, orcharacteristics. However, it should be noted that this is merely anillustrative example and claimed subject matter is not limited to thisexample. Furthermore, the term “at least one of” if used to associate alist, such as A, B, or C, can be interpreted to mean any combination ofA, B, and/or C, such as A, AB, AC, BC, AA, ABC, AAB, AABBCCC, etc.

Further, while certain embodiments have been described using aparticular combination of hardware and software, it should be recognizedthat other combinations of hardware and software are also possible.Certain embodiments may be implemented only in hardware, or only insoftware, or using combinations thereof. In one example, software may beimplemented with a computer program product containing computer programcode or instructions executable by one or more processors for performingany or all of the steps, operations, or processes described in thisdisclosure, where the computer program may be stored on a non-transitorycomputer readable medium. The various processes described herein can beimplemented on the same processor or different processors in anycombination.

Where devices, systems, components or modules are described as beingconfigured to perform certain operations or functions, suchconfiguration can be accomplished, for example, by designing electroniccircuits to perform the operation, by programming programmableelectronic circuits (such as microprocessors) to perform the operationsuch as by executing computer instructions or code, or processors orcores programmed to execute code or instructions stored on anon-transitory memory medium, or any combination thereof. Processes cancommunicate using a variety of techniques, including, but not limitedto, conventional techniques for inter-process communications, anddifferent pairs of processes may use different techniques, or the samepair of processes may use different techniques at different times.

The specification and drawings are, accordingly, to be regarded in anillustrative rather than a restrictive sense. It will, however, beevident that additions, subtractions, deletions, and other modificationsand changes may be made thereunto without departing from the broaderspirit and scope as set forth in the claims. Thus, although specificembodiments have been described, these are not intended to be limiting.Various modifications and equivalents are within the scope of thefollowing claims.

What is claimed is:
 1. A method of planarizing an overcoat layer over asurface-relief structure on a substrate, the method comprising: removinga portion of the overcoat layer using an ion beam at a glancing angle,wherein: the overcoat layer comprises: a plurality of planar surfaceportions; and a plurality of non-planar surface portions, wherein eachof the plurality of non-planar surface portions comprises a first slopedside and a second sloped side facing the first sloped side; the glancingangle is an angle between the ion beam and the plurality of planarsurface portions; and the glancing angle is selected such that the firstsloped side of each of the plurality of non-planar surface portions isshadowed from the ion beam by an adjacent planar surface portion of theplurality of planar surface portions such that the ion beam does notreach at least the first sloped side of each of the plurality ofnon-planar surface portions but reaches the second sloped side of eachof the plurality of non-planar surface portions.
 2. The method of claim1, wherein the plurality of non-planar surface portions are concave,wherein each of the plurality of non-planar surface portions furthercomprises a bottom between the first sloped side and the second slopedside, and wherein the glancing angle is further selected such that theion beam does not reach the bottom of each of the plurality ofnon-planar surface portions.
 3. The method of claim 1, wherein: thefirst sloped side of each of the plurality of non-planar surfaceportions is oriented at a first angle relative to the adjacent planarsurface portion of the plurality of planar surface portions; and theglancing angle is less than the first angle.
 4. The method of claim 1,wherein the glancing angle ranges between 1° and 15°.
 5. The method ofclaim 1, wherein removing the portion of the overcoat layer using theion beam comprises: reducing the glancing angle as the portion of theovercoat layer is being removed by the ion beam.
 6. The method of claim5, wherein the glancing angle is reduced from 15° to less than 1°. 7.The method of claim 1, wherein the surface-relief structure comprises aplurality of ridges slanted with respect to the substrate, and aplurality of grooves each between two adjacent ridges.
 8. The method ofclaim 7, wherein the plurality of grooves each have a depth that is atleast 100 nm.
 9. The method of claim 7, wherein the plurality of ridgeseach have a slant angle that is at least 45°.
 10. The method of claim 1,wherein the overcoat layer is deposited over the surface-reliefstructure using an atomic layer deposition process.
 11. A method offorming an overcoat layer over a surface-relief structure on asubstrate, the method comprising: receiving the substrate, wherein thesurface-relief structure comprises: a plurality of ridges slanted withrespect to the substrate; and a plurality of grooves each between twoadjacent ridges of the plurality of ridges; depositing, in a pluralityof processing cycles, a plurality of uniform layers of a first overcoatmaterial on surfaces of the plurality of ridges and bottoms of theplurality of grooves until the plurality of grooves is filled with thefirst overcoat material, wherein, in each processing cycle of theplurality of processing cycles, a respective uniform layer of theplurality of uniform layers of the first overcoat material is depositedon top surfaces and sidewall surfaces of the plurality of ridges and thebottoms of the plurality of grooves; and spin-coating a second overcoatmaterial on the plurality of uniform layers of the first overcoatmaterial deposited in the plurality of processing cycles.
 12. The methodof claim 11, wherein the plurality of ridges each have a slant anglethat is at least 45°.
 13. The method of claim 11, wherein only oneatomic layer of the first overcoat material is deposited in eachprocessing cycle of the plurality of processing cycles.
 14. The methodof claim 11, wherein a refractive index of the second overcoat materialmatches a refractive index of the first overcoat material.
 15. Themethod of claim 11, the method further comprising: removing the secondovercoat material deposited over the first overcoat material to exposethe first overcoat material deposited over the surface-relief structure;and removing a portion of the first overcoat material to obtain a planartop surface of the first overcoat material.
 16. The method of claim 15,wherein removing the second overcoat material and/or the portion of thefirst overcoat material comprises removing the second overcoat materialand/or the portion of the first overcoat material using achemical-mechanical polishing process.
 17. The method of claim 15,wherein removing the second overcoat material and/or the portion of thefirst overcoat material comprises removing the second overcoat materialand/or the portion of the first overcoat material using a glancing ionbeam etching.
 18. The method of claim 15, wherein removing the secondovercoat material and/or the portion of the first overcoat materialcomprises removing the second overcoat material and/or the portion ofthe first overcoat material using a dry etching process.
 19. The methodof claim 18, wherein the dry etching process etches the first overcoatmaterial and the second overcoat material at the same rate.
 20. Themethod of claim 11, further comprising, in each processing cycle of theplurality of processing cycles, after depositing the respective uniformlayer of the first overcoat material, removing portions of therespective uniform layer of the plurality of uniform layers of the firstovercoat material deposited on the top surfaces of the plurality ofridges.